Which option would you recommend?

[Pob255]

No they do use standard psu's just not ATX standard. (although the leads will often be custom length)
Just like Shuttle and almost ever other small form factor case.
The problem is finding out which standard it is and if PSU's in that standard are still being made.

Seasonic also make TFX standard psu's http://www.seasonic.com/product/pc_tfx.jsp

Be Quite do one, algthough I've a sneaking feelingg that they are made by FSP http://www.ebuyer.com/product/173802

And I includeded links for both the 9800gt and gts250 in my original post, granted one was ebay.

Before you rush out and buy anything open up that dell case and check the sized and form factors of the bits in side.
Some of the later cases use normal factor motherboard (mATX in some cases) with all the other bits (PSU and drives) crammed in in an odd way to keep the size down but exclude the option to use any slots.

We've got some viglen pc's at work which use the same cases as some of the SFF dells, the hard drive and psu both over hang the mATX motherboard meaning you cannot use any card over 6" long and the bottom 2 expansion slots are totally blocked.

[infernox]

the motherboard is a foxconn mATX motherboard. i have seen a video on youtube where some1 moved the motherboard and the components into a coolermaster case. i opened up the case recently to insert more ram and can tell that the inside of the inspiron 531s is the same as the inspiron 530s.

http://www.youtube.com/watch?v=EjTPwNigUIk

[Pob255]

Ahh it's the slim case not the SFF case, well if you want to replace the case with a standard ATX or mATX then it shouldn't be a problem.

[infernox]

well ive ended up just buying the sapphire 5570 from ebuyer. big upgrade from the 2400 pro and fairly good performance on 1280x1024. ive seen some overclocking reviews where it comes very close to the 5670 and even beats it sometimes. ill probably overclock is slightly at first and might overclock my cpu slightly aswell to see if my psu can take it.