Is it possible to dualboot two or more distributions?
 

I was just wondering, because I wanted to try slackware but I like Mandrake. Is there any way for me to download slackware and dualboot it with mandrake? If I do install slackware, would I be able to use the programs that i used with mandrake? Or would I have to reinstall them?

Dual booting them is no issue. Keeping the same apps could be tricky.

OK, I have two hard drives right now. the 175GB one is running Windows, the 40GB one is running Mandrake. I want to completely get rid of Windows. Can I reformat the 175GB hard drive, and use the 175GB for Mandrake and the 40GB for Slackware?

Well then you have to reformat both the hdd's and reinstall Mandrake and slack from scratch. You can back up the data on one hdd when formatting and installing on the other.