I have a Dell Dimension E510 that was originally loaded with
Windows XP. I have been unable to get my TV tuner card to
work with any of the distros I've tried (Fedora5, Frugalware,
Startcom).

When XP fouled up on me and I decided to switch to Slackware 12.1
only, I'm still left with trying to get the card to work.
Does anyone know if there is a Linux driver available?

As far as I can tell, the card is:
ATI TVT2-DT Wonder Elite Rev A00

Linux does not go by brand and model for each video capture device. Its video capture device module is like a unified structure. Just need to know the main chips the card uses for video capturing. List the brand and model of each chip of the video card. If that is too hard, use a scanner or camera to get a readable picture of the chips. I or someone else can read and suggest what to do. Using lspci also helps.

From reading Dell forum, the card uses Rage Theater 550. Rage Theater chips are not yet supported in Linux although Rage Theater 200 is supported. From what I read it is very limited.

The following cards that might work.

KWORLD PlusTV
KWORLD PlusTV HD PCI 120
SABRENT TV-PCIRC

They are based on either Philips SAA713x or Conexant chips.