As to whether removing the comments is possible, 
that depends on what kind of guestbook you've 
got.  I've also got an htmlgear guestbook, and 
you can edit or remove comments with it.
As for what I do with them..  Well, I hadn't had 
to worry about the problem until recently, when I 
finally got some chump with nothing better to 
do.  I decided to just leave it up, since it 
wasn't particularly vulgar, and I did put it up 
for anyone to voice their opinions, no matter how 
puerile or dull; on the other hand, they're 
really eyesores, and a waste of perfectly good 
space, so I can't imagine that I'd leave many up 
if I got more (which would require that my page 
ever got hits. ^.~;;;)
In the end, I'd say get a guestbook that lets you 
remove the pointless garbage, and just throw 'em 
out.

~Mala (Two posts in one day?  More than 20 
minutes of free time?  It's a miracle!)