PC system 3D CAD visualization, Precision T3400, T7400 ? graphic card

Hello specis,

as a non-specialist I am realizing after some days of reading through the Internet I NEED HELP.
I was made redundant in my job, so I am thinking of setting out of my own (single parent, food has to be on the table...), but my PC which I bought in Oct 2005 want not to be part of the deal. No way that it comes back to live affter the last crash.
Just before I was going to PC world I read here in the Forum, that this is not the place to go.

I am using the PC for 3D CAD / Visualization ArchiCAD, Microstation, SketchUP, AutoCAD Revit, Photoshop and MS Office (no gaming) .

At DELL I found this information on graphic cards for design application software:

For Industrial Design - Autodesk ImageStudio:

Processor: Dual, Quad Core Intel® Xeon® Processor X5482 (3.20GHz,2X6M L2,1600 FSB

Graphics card: 768MB PCIe x16 nVidia Quadro FX 4600, Dual Monitor DVI Capable

For Mainstream CAD - Autodesk - Inventor: Graphics card 768MB PCIe x16 nVidia Quadro FX 4600, Dual Monitor

For DCC - Design & Pre-Press - Adobe InDesign: Graphics card 512MB PCIe x16 nVidia Quadro FX1700

For DCC - Design & Pre-Press - Adobe PhotoShop: Graphics card 512MB PCIe x16 nVidia Quadro FX1700

For DCC - Video Editing - Adobe Production Premium CS3: Graphics card 512MB PCIe x16 nVidia Quadro FX1700

For DCC - Video Editing - Avid Xpress Pro: 512MB PCIe x16 nVidia Quadro FX1700

For DCC - Animation - Autodesk - 3ds Max: 768MB PCIe x16 nVidia Quadro FX 4600, Dual Monitor DVI Capable

For AEC/GIS - Bentley: PCIe x16 nVidia Quadro FX1700


Question: cheaper alternatives for a stable system? Would you recommend Precision T3400, Precision T7400 or R5400?

Many thanks in advance!

annamaria