DX is permanant, once you got it you keep it (that isn`t strictly true, there are some 3rd party apps to remove it..but they
can trash your system and AFAIK there are non done for 9.0b), try running a couple of the DB demo programs, and try removeing DB and then re-installing after a reboot, make sure you have your antivirus off while you install, AV`s are one of the worst offenders for trashing installs, also try re-installing DX, it`s not the first time someone has had a corrupted directx installation.
Mentor.
edit: what gfx card do you have?, you can check from control panel/system/device manager/display or right click the screen and select properties/settings and see what it says under display
PC1: P4 hyperthreading 3ghz, 1gig mem, 2x160gig hd`s, ATI radeon 9800 pro gfx, 6 way surround sound, PC2: AMD 1.2ghz, 512mb ram, FX5200 ultra gfx, stereo 16 bit soundblaster, ups.