Well, there really is no limit on how much software you can have on your machine, however, there are a couple "restrictions" if you will:
1) The hard disk on a computer will only hold a certain amount of data depending on how big it is. In this respect, one could call it a limit
2) Depending on the machine, one can only run a certain amount of programs at the same time before it bogs out.
If your machine is running dog slow (and based on your experiences with it, it should be running faster) here is my suggestion:
1) Read over this post:http://www.geekstogo..._Log-t2852.html
2) Based on the guidelines in the above post, start a thread in the Malware forum and the experts there will guide you thru cleaning things up if need be.