Yep.
On the day Rock Band 2 shimmies onto store shelves, Rock Band 1 will get an update that'll add an "export" option. It'll ask you for a password, which is included with your copy of Rock Band 2. After you punch in the code you'll have to pay up, but Harmonix says it won't be more than five bucks (the money is for rights holders). Then all of your songs, or at least the ones you're allowed to port (only 3 songs excluded), will be copied to your hard drive. Harmonix's PR dude John Drake also said that if you buy Rock Band 2 and just rent Rock Band 1, you'll probably be able to copy the songs as long as you pay the fee.