Hi Roffesenden, welcome to the Cameralabs forums!
Have you seen our group test which compares the Sony and Canon (and Nikon) models?
http://www.cameralabs.com/features/10Me ... DSLR_test/
You can see the noise performance for yourself in the results pages, but only you can decide if it's acceptable or not. Certainly at 800 and 1600 ISO the Sony will give a noisier result than the Canon or Nikon, but depending on the size of your print, you may not notice it too much.
And remember these are samples of JPEGs from the camera. You could smooth out noise, albeit at the cost of some detail, using programs like noise ninja, not to mention shoot in RAW for greater flexibility in post-processing.
One thing's for certain, the Sony's built in anti-shake will let you shoot at least 3 stops slower than normal, which could mean the difference of shooting at 100 or 200 ISO when the Canon would have to be at 400 or 800 ISO respectively. Of course fitting an IS lens to the Canon would give the same advantage, but it'll also increase your cost of entry.
If possible I suggest going to a friendly camera dealer with your own CF card and taking some photos with the A100 at all ISOs, then taking them home and printing them out. This will allow you to see for yourself how it performs. If you don't have a CF card yet, they might even lend you one for use in the shop then you could print them out there using their kiosk (or printing service), or perhaps burn the images onto a CD.
If you rarely shoot at 800 ISO or above though, I think noise will rarely be an issue for you with the A100 - especially with its anti-shake. And yep, you could of course also give yourself an extra stop or two with a brighter lens if necessary.