Here's the general troubleshooting KB article for that stop message:
http://support.microsoft.com/default.aspx?scid=kb;en-us;314063
Although there are formal troubleshooting steps in the article, sometimes it
is most useful to read the general causes noted and think about those.
In this case they list either newly installed hardware, or 3rd party
software or drivers as likely causes.
I think my next step would be to use MSCONFIG's startup tab to triage
third-party drivers and see if you can spot the conflict--start by disabling
all third-party drivers (if you use a third-party software firewall,
disconnect from the Internet) and re-enable gradually. Or, you can see if
you can spot a "likely" candidate--I tend to suspect video drivers (as a
general rule--not for your specifics, particularly)--or, in this case, the
third-party firewall if you have one.
Alternatively--you can see whether updated drivers are available for some of
those items.
Dell actually has an app which you can run which will tell you whether you
have drivers in place that are implicated in crashes as turned in to
Microsoft's online crash analysis system. I tried it out on a Dell laptop
last night and it did name a driver, but I haven't been able to follow up
and actually find a replacement driver--this laptop isn't, in fact, having
any problems!
The other option, of course, is to uninstall the beta, and test again when
another build is released.
This is a lot of testing to do, I know--but I hope it'll be of some use to
you, and maybe the answer will come quickly.
