I found a great deal on a PCI 64mb Geforce 4 MX 4000 to upgrade my Linux 633mhz Celeron, which doesn't have an AGP slot. I am hoping to use this for TT. And I am asking, will it run TT?

And I think there is an nVidia driver for Linux. (Fedora Core 3) If not I will just install a bare-bones copy of Win 98SE.

633mhz Celeron
256mb SDRAM
Expansion Slots: 1 PCI (It was an old tiny HP)
Fedora Core 3 Linux

CRAP! Turns out the pc only has a 100watt power supply, and since it's an HP it takes a certain kind. I need a card that runs TT, is PCI (NOT Express), and has a minimum of 100watts.

I found a PCI ATI Radeon 7000, will that run it?

Stick with nvidia for Linux. At least you will have a driver which will work with OpenGL and a card that isn't older than dirt.
I use a Nvidia 6600 chipset card for a linux box, mainly for the price. I compile the source and use Fedora Core 2. Check:
http://nvidia.com/content/drivers/drivers.asp

For drivers.

I'll be installing a copy of Win 98 anyway, but I will keep that in mind.

Guys these cards will be perfect to run in windows

Nvidia 7800 gtx (It's the latest and the expensive one, It can run huge games)
nvidia 6800 gt or ultra ( " )
ati radeon 9800 pro ( This ati card cost 200-350$ in some of the sites as I have heard)
Ati radeon 9700 Pro

Those cards rocks

These cards are cheaper with sufficient performance (good for small games)

Ati radeon 9200
Nvidia 4 mx 440
Nvidia geforce 3
Nvidia fx 5200
Nvidia fx 5500
And lots