Novell's web site has information about the new version of the GroupWise Mobile Server. The article indicates that it will likely be compatible with the Pre.
As you are all already aware, the core protocol is going to be ActiveSync, which means that any device with an ActiveSync client will be able to talk natively to GroupWise.
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We fully anticipate that Palm Pre will also eventually ship with an ActiveSync client in order to remain relevant in the handheld device market. We anticpate release towards the end of this year, though GMS continues to be supported by Novell in the interim, and we will give customers a migration window to make the cut over.