i agree it would be foolish to wait for vista. however, i have the beta 1 installed on a 32-bit pentium 4 downstairs (on its own partition) and it works fine. I will try putting it on my T42 and see if it works there also. Vista is going to run fine with most modern hardware. it will be a few years beyond vista before 64 bit becomes the norm.
for notebooks, i would strongly advise AGAINST buying an ultra-portable. People talk about lugging around weight and things like that - have you considered your books? the fact is, you are going to be typing on this thing, and your eyes will be fixated on the screen. I have an ultra-portable sony downstairs; it is a toy, and nothing more. i bought a ThinkPad for work and school purposes. its a good balance of everything.
don't buy an HP, Dell, Sony, or any of that other consumer crap. go to newegg.com and look at their T42s. T43 is the new model and does not offer any real advantage over T42 and costs a lot more.
IBM is simply a cut above when it comes to notebooks. i used to scoff at this, but after doing real research, i learned it was true. they are just built exceptionally well, from the keyboard to the display encasing to the display hinges. Don't buy a notebook without at least testing out an IBM T series.
I know Toshiba, Fujitsu, and Asus make good notebooks also.
Windows Vista has already slipped to 4th quarter 2006 ( http://www.networkworld.com/news/2005/072805-vista.html), and may very well slip further, based on Microsoft's history. Further, the only chips currently being produced that will run Vista are being built by AMD...meaning not a single Dell computer currently shipping will be satisfactory (since they only use Intel). More info: http://news.com.com/Could+HPs+AMD+laptop+sway+Dell/2100-1006_3-5760558.html. Even once Vista is out you'd have to wait for the school exam software to make the upgrade, which could take some time. To sum up, most current PCs are incompatible with Vista on a hardware level, so upgrades won't work for most users, even those with "current" systems. You mentioned some good reasons to put off the purchase, but waiting for Vista isn't one of them. FYI, if you're looking for Vista-compatible hardware, make sure you have a 64-bit processor in your system (such as the AMD Turion listed in the article).