Syncing iphone to a second computer

Hey guys, so here's the deal, i have an iphone 3G 8GB and have always synced my phone with my PC so my backup is in that computer.

Ive been out of the country for a while now and haven't been able to sync for a while (about 3 months) and I also have to update the iOS because i have the old 3.1.3.

So what I need to know is the following:

1-. How can i sync to a second PC without losing my data, specifically my contacts? (That's the only thing I actually care about, not the calendar, apps or any media) I don't use Microsoft Exchange, Google Contacts, Outlook, etc., on my old computer either so the only backup of my contacts is in my PC back home (assuming that contacts are backed up on PC just like everything else on phone when synced with itunes)

2-. Is there a way to update the iOS without losing data? (again only worried about my contacts, nothing else) If there is a way, I might just update the software and leave the backup part to when i get back home.

Please let me know if you can help me out!

Thx
Andreina.