"iTunes 7" dates from about 7 years ago. I presume you want 10.7 (you need to be precise here or we'll be pointing you to web sites with incorrect files).
You first need to update your Snow Leopard to 10.6.8, then iTunes 10.7 will install.
About the Mac OS X v10.6.8 Update - http://support.apple.com/kb/HT4561
Mac OS X 10.6.8 Update Combo v.1.1 - http://support.apple.com/kb/DL1399