I'm looking to upgrade to Windows 7 also on my 1535. I'm going from 32-bit to 64-bit. Is that your case? The upgrade advisor says everything should work fine with 64. I'm seeing a couple of issues online though with the ricoh driver and possibly the touch-sensitive media keys on the keyboard.
Did you or anyone else have problems installing windows 7 on the 1535? I'm looking forward to seeing the replies especially in regards to the media keys (pause, play, mute, etc.)