As the lone mac in a windows environment at my office, let me share my experiences with you a bit.
Get Office X. It's not great - you'll run into some issues now and again with Win users, but you don't honestly have much of an alternative yet. Keynote is great (instead of PPT) but compatibility issues still exist sending docs back and forth.
Entourage isn't half bad, but it has it's drawbacks. If you're using an Outlook server to get your e-mail and you need your IMAP folders (or you can't get your e-mail via POP) you basically have to have it.
You can share calendars with other outlook users etc but your company must have OWA installed. Many features are like this. And while you can send and receive invitations to calendar events, you can only accept events from people who are on your LDAP server. So if you don't have access to your LDAP server (like me) it's pretty useless. Furthermore, you cannot share or have tasks assigned to you - regardless of your configuration.
Finally, after using Entourage, my computer started to be painfully slow. It's unlikely, yet possible, that the performance issues are related to some other program, but I've decided to quit using Entourage completely. It seems handy, but for me, I could do everything I needed to in Outlook via OWA...which has to be installed for Entourage to have some of it's functionality.
In short, Entourage works, but for me, it was not worth the effort.
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UPGRADES - in my experience, Educational versions are eligible for future upgrades. This policy might change, but I've upgraded happily with no problems.
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Dreamweaver - while I love the program, it runs like a one-legged dog on the Mac. I've read countless similar accounts of this problem from people with dual 2ghz G5's. Buy it, but bring a lunch when using it. It's SLOW. I use MX, but I have heard that MX 04 is even worse. Overall, Macromedia's products do not work very well on Macs. Freehand (10) isn't so bad, but Flash MX and Dreamweaver MX don't always come to the front when you click the document, Dreamweaver is SLOW (as discussed) and Flash has a penchant for unexpectedly quitting on every machine I've ever used.. Save often in Flash.
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Best of luck!