ile be honest for that system 260 quid is rather steep as XP2400 athlon chips are quite old now, if it was a XP2800 or XP3200 barton core athlon my opinion would be different as there awsome cpu's
upgrades would be expensive as its a XP chip its a socket A motherboard which means you cant buy the cpu's from mainstreem retailers and there expensive to buy from ebay etc
will have an agp graphics card so again expensive and no so great upgrades as most stuff is pcie now
if i were you just buy a new system like this:
http://www.novatech.co.uk/novatech/specpage.html?PC-1102
260 odd with the os installed
brandnew 19inch tft for like 130 - 150 odd
that would give a pretty good system but if you wanted a better pc there are alot more options out there
my honest opinion its not worth anywhere near £260.00 more like £100 - £150.00 max.
system comparisons:
your one
150 gig hdd
Amd Athlon(tm) XP 2400+
2.00GHz
1gig ram (ram upgrades for 1gig its 30 - 40 quid)
windows xp
service Pack2 orginal
navida 6200a 256 ddr
monitor
£260.00
new system ive pointed out
AMD Athlon X2 4200 Dual Core 64 Bit
1GB DDR2 667MHz Single Channel (ram upgrade for 1gig 15 quid)
160GB SATA II hdd
NVIDIA 6100S PCI Express
vista home basic
£269.07 inc vat
massive differences in performance, upgrades etc but monitor at an extra cost