way to access iTunes 10 from an iPhone 5

When I plug my iPhone 5 into my 2008 iMac Intel to charge it says I have to upgrade to the newest iTunes software, and won't recognize it as a camera or a phone.  I've been loathe to upgrade because my 2005 iMac is where I have my main iTunes library and I'm afraid once I upgrade I won't be able to access that on the 2008 iMac with the updated software (the 2005 apparently can't be upgraded any further).  So I was thinking I would have to try and combine the two computers' iTunes libraries (each has the same account but different libraries).  But in reading some of this site, I was seeing that a lot of people greatly preferred their iTunes 10 and wish they hadn't upgraded.

Is there a way I can access my vast iTunes 10 libarary of music (80GB, mostly from CDs, LPs, etc. unavailable on iTunes store), as well as photos and apps, on my iPhone 5?