One easy solution is to drag & drop your music from your PC/Mac iTunes music library into your Palm Pre music folder manually.
The other official solution is to get MarkSpace Missing Sync software for Palm Pre and yes, it's been confirmed that even with iTunes 8.2.1, Missing Sync will still allow iTunes syncing with the Palm Pre. MarkSpace uses office Apple API for iTunes.
Keep your life in sync with The Missing Sync for Palm Pre from MarkSpace
By the way, MarkSpace makes multiple syncing software to allow multiple smartphones to sync with the Mac & PC.
The Missing Sync for Mobile Smartphones to Mac OS X and Windows
Also, the other solution is to use DoubleTwist made by "DVD Jon".
DoubleTwist Manages Your Pre Media, Freely, Easily, and Transparently | PreCentral.net
Or we can see what Palm will do when webOS 1.1 comes out later this month...