graphic card upgrade and hard drive advice

[heretec]

hi guys
im looking for a little bit of advise to make sure im going the right way about things im quite limited with my pc knowlege so any help appreciated.
my girlfriend bought a pc after the old one died it was built buy a so called enthusiast and its not run right since she got it ive found out the main problems with it and im currently looking to put it right .
my pc specs and problems
abit is7-g mobo
p4 2.8ghz (turns out its mobile p4 wont go above 1.6ghz locked multiplier)
ge force fx5200
120gb maxtor ata (ide) failing

im ok with the cpu im getting a p4 3ghz (non mobile lol) the graphics card needs updating im not a hardcore gamer so im not bothered with high end ,i looked at a Asus Radeon HD3450 512MB Low Profile AGP Graphics Card and wondered if it would be compatible and ok .my next issue is the failing hard drive should i replace it with the same type ata or can i put in a sata and would that be a better choice all advice greatly appreciated thank you

[Terbinator]

What's the PSU in this build. We could also do with an overall budget as it may be possible to build a whole new rig that will be a lot faster for not a lot of £££.

[heretec]

hi terbinator thanx for the reply
the power supply is atx 500w 12v for pentium 4,the budget isnt that big im afraid the pc is only a few months old so i was looking to just sort out the problems at the moment my budget isnt that great but if you have some suggestions i could always see what i could stretch to also if i have to order anything it has to be from europe or uk (prefered) impoting from us isnt an option as ontop of import costs we have to pay a tax for us imports , i live on a tiny island so that doesnt help with importin cost lol
thank you very much for the help