Forget Aero. Whether you run it or not, running Vista with any degree of comfort is all about screen real estate. Technically your system may run Vista fine, but don’t forget that it also takes up more of your screen than ever before with its larger desktop icons, task bar and new sidebar. Even aero adds a few more pixels per window to its borders. So beware.
Having just fallen foul of this myself (and big ups to Dell Customer Support for their cracking service during the whole self-imposed debacle), here’s my thought for the day. Buy the best screen with the highest resolution you can afford. Even if you don’t play games, your first impression of Vista will be its user interface which Microsoft has worked hard to improve and is justifiably proud of. Using it with a crap screen will not help matters.