Hey joeboxer!!
Welcome to aximsite
The good news is I assume you have a X51V (not a v51 lol) so hopefully Dell will fix this soon.
Anyway since you have WM5, the Bluetooth manager doesn't exist. The previous version of Windows Mobile (WM2003) used a different Bluetooth stack, or drivers if you will. IMO the stack used in WM2003 is far superior to the stack used in WM5. Don't worry all X51 users are stuck in the same boat. There have been numerous attempts to fix, but no luck so far.
BTW I would recomend just buying a Wireless Router. Gets better range, and its faster when surfing the Internet.