10.0B isn't supported on Server 2008. You need at least 10.1B for Server 2008, and at least 10.1C for Server 2008 R2. There is some ambiguity on this in the current Product Availability Guide (
http://download.progress.com/open/openedge/pag/openedge_10_availability_guide_2011_05_06.pdf). The information on pages 2 and 6 seems mutually contradictory. Product Support told me to look at page 2 (the more restrictive of the two), and that they will remove the ambiguity in the next release of the guide.
I believe OE Explorer was introduced in 10.2A. If you need Progress Explorer you can run it on a different computer with an older, supported OS (see note N in the guide).
Anyway, I'm with Tom. Upgrade if you can. If Windows is your choice (or your only option), go with the 64-bit database on Server 2008 R2.