Yer main problems is memory when yeh get wotlk its gonna get worse.

from the starter area to the normal-outlands-northrend require progressively more memory

go to start-control panel-system under the advanced tab- performance- settings click on adjust for best performance and hit apply

another thing yeh can do is stop a bunch of the services that are running that arent needed but yer gonna have to the some research to find out what yer can stop and what yeh cant.
This frees up some memory and cpu cycles.

another thing is start-all programs-startup and remove whats there.