Hi martynshortWLA
The Mesh Elite D8 is not in their current range so it is not possible to check on the full system specs to ensure that any graphics card recommended is compatable with the rest of your system.
If you could post back with some more information about the motherboard and power supply especially it would be appreciated. As an initial guide, assuming you have a motherboard that supports PCIx and a powerful enough power supply something like a HD3650
here is a good choice. It has 512mb of dedicated graphics memory so freeing up resources on the rest of your system (especially important as Photoshop is a very memory intensive application) and two DVI outputs allowing you to connect dual monitors. It is also a very good price.
If you would prefer something a bit more powerful post back with your maximum budget.