in reply to using regex to not match a string

Oops. Didn't notice the ; at the end of the pattern you want to avoid.

What Tanktalus said: /&(?!amp;)/ .

/&(?!amp\b)/
The above will match &, &foo, &ersand, but not & followed by a \W character or by the end of the string. If you don't want to match &, irrespective of what follows it, then use
/&(?!amp)/
See ?! in perlre.

the lowliest monk