Originally Posted by Halo
It's unlikely that one anti-virus program is going to perform a full scan much faster than any other.
The average computer has over 1 million files on the hard drive. During a full scan each file must be read from the disk and then analyzed to see if it's infected. Modern computers are so fast that the analysis is nearly instantaneous. It's the reading of the data from the disk that is slow. That bottleneck won't disappear when you switch anti-virus programs. All of your data must still be read from disk no matter which program does the full scan.
If the full scan is impacting your work day, you can configure it to happen automatically at a different time. Open Security Essentials, click on the Settings tab, then click on Scheduled Scan on the left side. You can then change the settings so that the scan is done in the middle of the night. If your computer is asleep, it will wake up at the configured time, perform the scan, then go back to sleep. See the screen shot that I've attached to this post.
I realize this is an answer to a question you didn't ask, but I thought I'd share it anyway in case it's useful.
Thanks Halo. Yes, I think this is going to be perfect for me. I went and set my Microsoft Security Essentials exactly like you have it in your screenshot. I do have a question about what you mean by the computer being "asleep." My computer is on a Memorex "Power Center." I've got the scan set for Sat. 4 a.m., so I was figuring I need to leave the "Power Center" on Friday night, but do I shut the computer down? I'm not familiar with a sleep setting if there is such a thing. (I've got XP.) I think this is going to be good. Thanks again for suggesting it.