Upgraded Tiger/Parallels 2.5 to Leopard/3.0 build 5582: Now what?

I upgraded a Macbook (2Gb, 160Gb disk) from Tiger to Leopard and from Parallels Desktop 2.5 to 3.0 Build 5582. Now I find that performance in parallels is poor, and when running an old game that runs in DOS box, Parallels is using over 100% CPU even when doing nothing!

I just saw a note saying that upgrades from 2.5 to 3.0 should use a release *before* Build 5582 on Leopard. Of course the installation didn't give any errors or guidance, but now I am concerned that this might be an issue.

My questions:
1. What are the issues that cause the advice to upgrade from 2.5 to 3.0 using a non-5582 build

2. Would these issues contribute to the performance problem?

3. Does Desktop 3.0 and/or Build 5582 have know issues with DOS apps (I couldn't find any in the various FAQs).

Any and all pointers much appreciated. My wife, previously very happy with Parallels is now most unhappy - not good for Christmas Day!

Cheers, --Kip