I have a couple more thoughts for you.
As you have explained, you are committed to making this work so there is no point in rehashing whether our not making the switch was a good decision.
I'm a small business person myself, so I have some idea of what you are going through - and sympathies.
1) Don't sweat the sized of the text in the menu bar.... pretty soon you won't even really be reading it. Concentrate on the bigger problems.
2) Make back-up copies of all of your important files now, and put them away. While you are migrating your information back and forth, and working with the Sony to do some things and the Mac to do other things the probability of overwriting a file increases. Your data files are critically important.
3) Get a Mac Guru... ask around your friends and find someone who speaks normal language (not geekese) and will help you with the switch. I do this for my friends and acquaintances - and what I do is ask my clients for each session to prioritize what they need to learn immediately. Its too tempting to try to learn (and teach) too much at once. e.g. Your guru should show you how to make Mail do what you need it to do. They should, ideally, sit to the side and talk you through it ... and let you take notes. Once you have learned how to work Mail, then go to the next thing.... and then send the Guru home for a few days. In the next few days you should practice what you learned, and then at the next session you can ask follow-up questions plus add something new.
I don't think you will need more than a few sessions.... your needs aren't that complicated (despite what it feels like right now). I know you feel that you don't have the time for this, but if you don't you are going to prolong the switching misery. Do you have time to be banging your head over simple tasks for the next few months?
As you are discovering, Macs are not Windows - and despite the marketing, Macs don't do everything that a Window's system does. On the other hand, Macs do things that Windows can't... you just don't know what they are yet. Once you have fully made the switch, start discovering what a Mac can do.
One of the things I love about my Mac is that I can create a family of advertizing material that all look the same very quickly. Because so much of the Mac is 'drag-n-drop' I can create ads, brochures, up-date my website, create a price-list, make an artist statement, send out a press-release, etc etc using several different applications but still using the same text, images, keeping the same 'look and feel', etc. very very quickly.
Good Luck. Keep your spirits up.... find that Guru.
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We tried around it a bit, and eventually the 'high-tech' got involved and the problem is that there are multiple POP, IMAP and a 3rd which I can't remember, are involved. He said it is a fact that on POP only the INBOX will download, it will not sync, so if you read it on the MAC it will still show as unread on the server. ... .
I'm using 10.5.8, and I'm guessing you are using 'Snow Leopard', 10.6.x - but I believe Mail will be the same...
Open Mail, then go Mail's preferences. Go to Accounts, and you should see your email accounts listed down the left side. Click on one of your POP accounts. You should see, along the top of the right hand pane - "Account Information", "Mailbox Behaviours", and "Advanced". Click on 'Advanced'. One of the check boxes should allow you to "remove copy from server when retrieving message." If you enable this, then it will remove it from the inbox of your server. However, it may take a day for your server to change the status. If your server is moving "read" messages from the server's inbox to the server's 'read' folder then you may have change a setting on the server to stop that behaviour or to purge the 'read' folder after a day or two so you don't go over any storage limits your server may have.
Also, you may want to play with the 'Mailbox Behaviours' a bit... but don't change everything all at once because if something doesn't work as you expected it will be impossible to figure out what went wrong.
In Mail Preferences you can turn off Junk Mail filtering. If your email provider is filtering spam you may be able to get away with this. There are also ways to customize Junk Mail filtering that may better suit your needs.
I use Mail rules to do my initial mail sorting. I have about half a dozen email addresses that all go to my inbox unless a message meets certain criteria, in which case it goes to the appropriate folder so I can watch emails that relate to specific groups or people.
Once you understand about "Smart Folders" in the Address Book, you can use the Address Book as a simple data base for your addresses. "Smart Folders" (in the Address Book) allow you group addresses/contacts based on a set of rules. It is a filter that matches the criteria in real time, and therefore is always up-to-date (in theory - not always in practice... sometimes you have close Address Book to make the changes 'stick'). I've set up a bunch of code words that I insert into 'Note' section that allows me sort based on my own criteria, and not just the built in fields. I do mail-outs on a regular basis, and can send emails to just the groups that have expressed an interest in a particular project.
Hope this all helps.