Question : Problem: Can I re-install Vista OEM due to a fried Motherboard?

I installed Vista Home Premium OEM on a clients computer last year, and now his mobo has fried.

All other parts are fine and I also have an Acronis disk image of the original install and the OEM disk.

The HDD is fine also.

What's the best way to get up and running with a new mobo or do I need a new Vista OEM because of activation problems?

Answer : Problem: Can I re-install Vista OEM due to a fried Motherboard?

To answer your question, simply install the motherboard and boot up the machine.  (it should really be that simple)
I had an Vista machine using a 925X chipset in a dell 4300, installed a new motherboard after that one had died, it had a P965 chipset, it was more like i built a new computer all together.
To my surprise, Vista booted up, didn't complain about motherboard drivers.  Asked me to reactivate, i had to call MS to get a code since i had had to reinstall vista several times on that machine before we narrowed it down to the MB.

So, don't worry about the new hardware, if windows deactivates, it should reactivate when you activate the license again after you've got all the problems worked out.  If it doesn't, give MS a call and they "should" provide you with a code without much trouble.  I've never had them question me or deny me activation so i don't expect they would you.