You're obviously limited by the 350D's sensor, but it sounds like you're on the right track. Open up the aperture as much as you can (lower the number - possibly only goes to down/open to f4.5 on the lens you're using) and crank the iso as high as you can without getting too much noise.
If you've got photoshop, you've got more room to move.
Shoot at even higher iso's and use noiseninja to clean them up, or shoot in raw, underexpose a bit and then use PS to correct the exposure.
Aside from that, it may be time for an upgrade.

EDIT: just read what lens you're using. Ignore what I said about aperture.

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