I am using Photoshop 5.0 (the old, old one).
I have Photoshop 6, 7, CS2, CS3, CS4 on a virtual machine (to support others) and CS5 on my main system and you happen to have 5...bummer, otherwise I could have told you the exact steps, because there have been some huge changes between 5 and 6.
EDIT:
Ok, I decided to do you a little New Year's favor by installing PS 5 to know exactly what we're dealing with, because it has been a long time ago that I had a look at this version of Photoshop.
Go to
Select / Color Range and use the settings in the screenshot below and make sure that
Yellows is selected beside the entry that reads
Select. Press
OK and press the
delete key to remove the background.
Does the result satisfy you? Personally I think it's pretty good and if it's not good enough for you, then I have to show you a slightly more advanced technique. Normally I would never advise people to use the delete key, but in this case I wanted to keep it simple.
So let me know what you think.