Yes you can use several anti-spyware programs, although it's best not to use more than one that tries to stop spyware coming into the system (ie runs all the time).
If they're the type you just scan when you wish to, then it really doesn't matter how many you have.
I have the Eset security suite - and I also run Adaware and Spybot from time to time. These days though they find next to nothing, and what they do find is of little consequence, as the Eset suite is pretty good.
On odd occasions I've tried out other programs too, on a once off basis. Nothing found by them either.