Not much info to work with. My guess(tm) is that some program, process, daemon, worm, virus, or buggy driver is stealing CPU cycles. Since you didn't disclose your operating system, I'll assume XP Home.
Do you have TWO wireless devices? The Acer Travelmate 291xci laptop includes an integrated wireless card. Now you're adding another wireless (WG511TGE) card? Why?
Fire up the Task Manager (hit alt-ctrl-del and select task manager). Go to the "Performance" tab. With the machine at idle, the cpu usage should be very very low (about 1-5%). My guess is that you'll find that it's running considerably higher than that. If so, look at the "applications" and "processes" tab and try to determine which application or processes is hogging all your CPU cycles. My guess(tm) is that you have a worm or spyware that's detecting a wireless internet connection and making the CPU rather busy. I suggest downloading and installing Microsloth Anti-Spyware Beta 1 which I've found works much better than anything else I've tried.
On a different note, there have been several important updates to the Centrino wireless drivers. XP SP2 also adds considerable improvements to the Wireless Zero Config drivers and program. I suggest you update both, but only AFTER you stabilize the laptop and remove whatever is causing the CPU/mouse/whatever problem.