I'm running Vista since my school is "upgrading" everything to Vista and Office 2007. It is OK, but I would not run with less than 2GB of RAM, preferably with 3 or 4GB. I have 4Gb on my laptop and the minimum configuration at school comes with 3GB. I would definitely stick to XP if I did not have to upgrade.

Vista makes connecting to networks more obscure to me, it has a few niceties, but in general it is not a substantial change. It is a bit of a pain with some software that has not been updated for Vista (for example, SAS), forcing one to install and run in WinXP compatibility mode as an administrator. It won't affect Office 2003, but if you upgrade to Office 2007, there is a learning curve: the programs look very different. And then there is the "65535" display bug in Excel... multiplying 850*77.1 results in 100,000, not 65535. It is only a display error (if you use the result in another calculation, the result will be correct), but it makes me wonder what else is broken.