Download the 1.1 patch. This patch issues the sound problem, among others.
That's one odd problem. I have GTA San Andreas in my Windows 7 Ultimate, and it works like a charm (with mods). Try the 1.1 patch and be sure the drivers
for your mouse up-to-date and functioning well (if you're using an Intel mobo/GPU, the INF should be functioning properly). Better yet, try asking in GTAForums.