I think it really depends on how much the difference is between the two. Win 7 seems to work OK with 2 GB of RAM, where XP works OK with as little as 500 MB RAM (plenty of older systems came with 500 MB, from Dell and so on).
Nowadays, many systems come with 1 GB of RAM (the poor uptake of Vista meant Microsoft extended the life of XP, and it was additionally licenced to run on Nettop machines such as the Asus EEE box, MSI Wind, and more recently the Acer Revo
(Nettop boxes are suitable for playing films on your TV, have a 1 GHz CPU - OK for doing single task at a time rather than running several different applications at once - and usually include 160 GB to 500 GB of disk space and wi-fi as standard). As well as XP, there were some Linux boxes, but quite soon after they came out, Microsoft must have allowed the manufacturers to include OEM versions of XP, while others like Dell were offering a 'downgrade' option (for a fee) to keep running XP.
Assuming this notebook might be replaced in 2 to 3 years, XP would (in my view) be just as usable as Windows 7, as many of the changes will have been cosmetic. If the price difference is under 50 quid it may be worth going for the Win 7 model (out of interest, which ones have you looked at please?)
One problem I had (before giving my Win 7 laptop to my sister) was that when I used a multimedia USB keyboard, on Win 7 it acted at intervals as if I had typed dozens of random characters, but works fine now it is back in an XP laptop. I have 2 or 3 of these multimedia keyboards and tried all, but all had the same problem, so the basic Win 7 driver may have a bug.
I'd add AVG (free) anti-virus with either XP or Win 7. Service Pack 3 (SP3) is still available for download for Win XP, if it isn't already installed, and various other small security updates for 32-bit systems will still be available for some time yet.
0 anti-virus