Xenserver adding a vCPU to a Windows server

[cookie_monster]

I've have a couple of Citrix boxes on a Xenserver with one core of a E5440 processor each, I decided they could do with another vCPU so I added another in Xenserver but it doesn't seem to show properly.
I see nothing about a change of hardware in the Windows event log and systeminfo lists one CPU but if I look in device manager I can see 2 E5440 CPU's listed.
If I look in task manager on other multi core or hyperthreaded boxes I see a box showing how busy each core/CPU is but on this Citrix box I only see one CPU listed.

Have I missed a configuration?

I'm wondering if this could be a HAL issue.

The server is running 2003 Server SP2

Thanks.

EDIT

I can see now that it is a HAL issue the server lists itself as uniprocessor free not multiprocessor free. Some reading is required I think.

[cookie_monster]

All sorted. I forgot it's Windows, a couple of reboots were in order

The HAL driver isn't updated until the 2nd CPU is detected so you have to reboot again to load the new HAL allowing Windows to use the CPU.