2008 (non-R2) had native drivers for the PERC 4e/Di, but 2008 R2 did not (Microsoft removed native support for SCSIport devices - going forward, these devices will not be supported out-of-the-box by Microsoft).   Dell is not yet selling Server 2012 and they have yet to publish any needed drivers for it, but the 2008 R2 drivers should work better: www.dell.com/.../poweredge-2800 More information - it is currently validated internally on 9G systems and newer, but drivers have not yet been published; unclear whether they intend to support it on 8G (that doesn't necessarily mean it won't work): en.community.dell.com/.../3492.windows-server-2012-inbox-driver-support-on-dell-poweredge-servers.aspx
I have a PowerEdge 2800 with a  PERC 4e/Di that I use as a lab computer.  It had Windows Server 2008 R2 installed (which is x64), and today I wiped it and attempted to install Windows Server 2012 RTM.  Guess what?  There's no driver support for this system with 2012 RTM.  As I recall, driver support was included with 2008 R2.  After some digging around, I was able to download the Windows Server 2003 x64 driver from the Dell website, and now I've got 2012 installing.  Seriously, how lame is that? It wouldn't have taken much effort for MS to include driver support for the PE 2800 and similar older, but very capable systems, especially since the drivers already exist in most cases.  FWIW, it doesn't look like 2012 supports the PE 2900 either, which is hardly a dinosaur.  Or how about Dell extending the life of these systems with some driver updates? Getting up to speed on a major new OS is a very big undertaking on many levels.  Do we have to go buy all new hardware too, just for a lab eval?  There are thousands of IT shops with older, but very capable systems, which we've spent lots of $$$ on.  Making a new OS accessible to these systems lets people like myself get learning and testing the new OS with virtually no cash outlay.  It's a win-win.  Unfortunately, vendors are very shortsighted in this area. Anyway, if you're looking to get 2012 running on the PE 2800, try the W2K3 driver.
Windows Server 2012 on PowerEdge 2800