Updated information: The BIOS on the Dell t105 will not allow any NVIDIA graphics cards in any of the PCI or PCIe slots. The BIOS becomes unreadable because you have both the added graphic card and the on board graphics enabled (and the on board cannot be disabled!) IT WILL NOT WORK WITH ANY PCI CARD!
Per the specs in the getting started guide the T105 has only 1 x PCI, 1 x PCIe 1x and 2 x PCIe 8x slots.
As most videocard are PCIe 16x (and I have never seen PCIe 8x videocard), you can't use any of those. You're limited to PCIe 1x videocards, which is a short list or PCI cards, which is a longer list, but generally older type videocards.
No, this isn't right. You can use a PCIe-Lane Converter from 8x to 16x and you can use then almost any card you want. I have converted my PE1900 to a power workstation by silencing the fans and using a PCIe-Lane Converter to run a PCIe-Graphics-Card. I use the Radeon HD4670 because it is the fastest available card without additional power-connectors.
You can read it here: http://en.community.dell.com/forums/p/19245382/19383665.aspx
The adapter you need is this one: http://www.orbitmicro.com/global/pciexpressx8tox16adapter-p-755.html
And my new graphic card is this one: http://geizhals.at/a368175.html
Also older PCI video cards would work:
Howto for fglrx (Ati driver) and Compiz / Fusion