Your going to have to take a different approach.
The logo in the overall header in the Helius theme in the Forums is actually two parts.
logo1.gif
and
logo2.gif

Restore everythign back to the way it was for now. You'll have to rethink how you can get your own logo in there.
You may have to strip down the overall header file or rebuild the html part to suit your needs. I can't do it FOR you since this is a personally preference and customization. The best I can do is give you advice :-)

mikem