2nd HD for dwnlds/protect primary from malware?

hello friends-i hope my title makes some sense. i wanted it to convey what i was asking about so people browsing could tell. cuz i couldn't find a question like mine.

i have a new hd completely installed and setup. my old hard drive is now the secondary master and although i still have the OS and programs installed, i never use it. lately i have been actively file-sharing via lime wire. i am behind a zone alarm firewall and running spyware blaster and AVG free. i also regularly scan with spybot S&D. i also scan each file with AVG b4 opening (thanks to majorgeeks for advising me on security)
however, i've been warned the limewire is notoriously risky as far as spyware etc. so my question is:

If i choose to open my secondary OS at start up, and browse and download these risky files to my secondary HD. will that protect my primary HD from infection?

if not, any other advice u have regarding the risks of file sharing are appreciated.

one thing i look out for is files that are too small to contain what they say they do. for example 100kb song files. i just dont download these.

 

yes, you did answer what i needed. awesome answer actually. my question was initially inspired by my determination to put my old HD to some worthwhile use. and now i have an answer to that too. :> thankyou. you guys rock.