Upgrade to the latest kernel 2.6.17-1.2174_FC5,  so far so good...? 
I had all kinds of problems too with 2.6.17-1.2174_FC5, random reboots,
random crashes, network problems, etc.....  You''re problem is probably
NOT CUPS related, but xen!
If you still have problems, use 2.6.17-1.2139_FC5.  Worked well for me.
Well, still,  Xen rocks!
Robert
On Fri, 2006-08-11 at 18:08 -0400, Rik van Riel wrote:> J.L. Coenders wrote:
> > Hi,
> > 
> > Has anyone tried printing with CUPS on the fc5 Xen kernel 
> > (2.6.17-1.2157_FC5xen0)? 
> > I was trying out Xen and it seems to crash my system. 
> 
> Works for me.
> 
> What kind of printer?  Parallel port?  USB?
>