are you gonna be using it on battery or mostly mains? difference is, if you use it on mains you will get a much more powerful lappy (just s*d all battery life).
i would say spec-wise try and get 512Mb RAM but its very difficult at that price. if you get 256Mb, make sure its 'DDR' RAM (double data rate, quicker). dont go for anything less than a 2200+ Athlon or 2.0Ghz Pentium 4. i dont know if you need a good graphics card or not for your work but best ensure you get 32Mb or more graphics and make sure it doesnt share the main RAM for best performance.
Software-wise its always good to get the MS Works Suite that has Word 2002 in it for your assignments - preferably included with the lappy as its about £99 or so.