The A100 was good at ISO 100 and 200, decent at 400, but I really tried hard to avoid ISO 800+. I replaced my kit lens with the
Minolta 28-75 f2.8 and it worked great for low light, and still gave me a good zoom range. If you want to save some money, look for the
Minolta 50mm f1.7. There are a couple
versions out there, and can usually be found for $80 or so. Once I started using the 50 f1.7 a lot, I upgraded to the Sony 50 f1.4. I LOVE the 1.4. The lens performance is awesome.
Also, for the longer ranges, check out the
Minolta 70-210 f4 aka Beercan. These can usually be picked up for under $200.
The other option would be to change Sony bodies if you wanted to stick with them. I picked up an A700 when it was released and sold my A100 immediately after. Obviously, it costs a little more. The A200 that is out is an upgraded A100. It used the same 10.2MP sensor, but does a better job handling noise at higher ISOs, has ergos closer to the A700, and can now be had at the retail price of $500 for the kit.
I do still have my 28-75 f2.8, a pair of 50 f1.7s and a 70-210 f4 if you are ever in the Dickinson area and wanted to check them out. I don't use any of the 3 much anymore since I have the 16-80Z, 50 f1.4 and 70-200 f2.8.