If you not seeing the problem in XP mode then it's your system, not your provider, and specifically an issue with W7. It likely is a process which launches when you're in game. Open task manager and check Processes for anything which is constantly making a CPU or memory demand - there shouldn't be one. If you see one Google it to see what it is before you shut it down. Since you're running a bootleg copy of W7 and you told me you're not running anti-virus software, it would be a miracle if you've not been hacked or loaded with viruses and Trojans.
If you don't see some service continuously running leave Processes tab open as you do your various 'puter stuff and look for a burst of CPU usage from something at sporadic times. Don't start closing Processes or Services arbitrarily. As I said in game, lots of folks attempt to continuously tweak their systems to get every bit of open memory/CPU they can, to the point they do serious damage to the OS; overtweaking doesn't make the game run any faster.