Moving from one user account to another, questions

I spent about four hours with customer support between the phone and instant message support a few days ago. I have a dot mac account, and use the Mail app. It has stopped working. It works on my iphone, it works on webmail, but the Mail app does not.
Other computers in the house using dot mac and Mail work fine. I can't get the Mail app to connect to any email accounts, such as gmail either.
Phone support moved me up 3 levels of folks to talk to, we spent a couple hours on the phone. Finally, fixed. Like four days later, it's gone again. I don't quite remember what all we ended up doing.

iPhoto doesn't work. It will for a while. Then I get an error message and it just hangs. This was months ago, I gave up. Support couldn't solve it, I think I asked here too and never got it figured out. I switched to Picasa and have been happy since it never seems to mess up.

During the time when the iPHoto thing was bugging me, I totally wiped out the machine and started fresh. All the problems returned in no time.

So I know I can call support back. But I get the feeling this is all just going to keep happening. The computer was purchased in 2007, running 10.6.2 (imac). It's all updated, etc.

If I make a new user account, is it possible IT wont have these errors? Or is this a system wide thing?
I know having dot mac will move most of my things along for me, mail, address book, ical, bookmarks, dock items, etc. But what about Picasa? I spent months and months organizing that. I suppose there is no way to just shove it over to another user account as is? I have an external... which is a mess of duplicate files and a lack of organization. But I do have one, and I am going to guess that is how I have to move things? I just lose all of my organization and such?

I'm starting to understand why people are moving to all web based apps. I am sick of nothing working. I love the Mail app though. Just love it. But I don't want to have to "fix" it every couple days.

Any thoughts or help much appreciated.