On Windows2003 Server R2 performance of IS becomes slow.

We upgraded our OS from win2003 Server SP1 to win2003 Server R2.After the upgrade the performance of IS became very slow.File read/write now takes more than double time than before.Everything works fine when we again test it with win2003 Server SP1.
After doing some research we found that it is not a problem of Operating System but something is wrong with IS.
Is WebMethods IS compatible with win2003 Server R2?Are there any special settings to be done?

Thanks