I read some were that Microsoft has stopped asking for proof of "student/teacher" status as they estimate that that at least 80% of UK house holds have at least one member of the family that would qualify. Bering in mind that a lot of adults attend evening classes and they are classed as a student. As for the limitations of the "student / teachers" package, I would not recommend the full version as if is just not worth it. The Student version will do just about every thing you could ask for.
If you need Access, Ebuyer.com do a Student Pro version, and are probably among the cheapest for the straight version as well.
As for messing up email accounts, for what its worth I just updgraded from Office 97 to Office XP. I left 97 installed and installed XP over it. It picked up all my internet accounts, and moved all my contacts and message from Outlook. The only thing it didn't do was copy accross my e-mail passwords, so reminde yourself what they are before you make the upgrade.