My current system has the following specifications:
Model: Dell Dimension 9200 (XPS410)
Windows Edition: Windows Vista Home Premium 32-bit
Processor: Intel Core QUAD Q6600 SLACR 2.40 GHZ/8M/1066/05A
Mainboard: Dell OCT017
Video Card: NVIDIA GeForce 7900 GS 256mb (Dimensions: 190x100x15mm)
Sound Card: Creative Sound Blaster X-Fi Titanium Fatal1ty Sound Card
Hard drive: 320.00GB (2x160gb) serial ATA (7200 Rpm)
PSU: L375P-00 DELL 375W POWER SUPPLY KH624
Memory (Ram): 4.00GB (4 X 1GB PC2-5300 667MHz DDR2 SDRAM 240pin)
Monitor: Dell Ultrasharp U2410
Video type: PCI Express
Expansion Bus: PCI x 3, PCI Express one x1, PCI Express one x4, and a PCI Express one x16
Your main problem with getting a better graphics card is the 375W power supply. It's marginal for cards even in the mid-range. Go to the link below (it's a PSU calculator) and plug in the values based on your system and add one of the cards in the 2nd link to see if your PSU can even hande one of them. The 2nd link is to a U.S. site, so you will have to convert dollars to pounds. But the range I listed is about your stated amount in Dollars. Finally, the last link is to Tom's graphics card hierarchy chart, so you can see where your card and new ones rank.
Thanks for the links. It looks like i'm going to need at least 450w for the GTX 460 or HD 6850. I think I may need to look at upgrading my PSU.
A wise choice, but be aware that Dell uses or has used proprietary power supplies. The wiring between the PSU and the motherboard is slightly different than standard. You may have to invest in a Dell branded PSU. Maybe someone else can expand on this, as my knowledge on the subject of Dell machines is limited.