if i haven't paid my '08 car taxes, can i still register my new car? or will they make me pay them?

In California:

You pay tax on the purchase called a USE TAX, and you pay that at the time of title transfer. Have you transfered the title into your name yet? Because you must pay all fees before they will issue a new registration. You will additionally be penalized for not transfering the title into your name after 10 days.

I would go in and pay something, anything. At least pay the $15 fee for title transfer. Begin the process.

Are the tags current? They won't give you tags until all paperwork and fees are paid and coomplete.

I doubt it very much; DMVs have long memories. Just hope your tax refund will cover both years.