Can You Run Malwarebytes With Another Anti Virus Or Anti Spyware Program Already On Your Computer?

I’m thinking about ditching Windows Defender because I know it sucks, and it came with Norton Internet Security 2008, and I know I have talked bad about Norton, but they have improved greatly from the past, and it doesn’t slow my laptop.
I’ve read and heard so many great reviews about it, so if I have Norton, Super anti spyware, can I run malwarebytes along with them?

Can I Use Peer Guardian With The Firewalls I Already Have?

I have a mcafee firewall and i think i also have a firewall in vista as well but i am not sure can i use peer guardian with this?

How Do I Remove Registry Files/keys When The Program Is Already Deleted?

ok so i deleted a couple programs and they still show up in my start menu. i go into Regedit and i hit Ctrl+F and i type in the program. is there a program to remove the left over registry keys?