You should be able to use the 4.x SDK to develop 3.5 apps; as much as we can make them, the SDKs are backward compatible.
As for APIs to avoid (that is, ones that were introduced post-3.5), see the "Compatibility Guide" appendix in the Palm OS Programmer's API Reference. In particular, the "4.0 New Feature Set" section lists everything introduced in 4.0. -Greg Wilson Developer Services PalmSource, Inc. -- For information on using the Palm Developer Forums, or to unsubscribe, please see http://www.palmos.com/dev/support/forums/
