There is two work arounds i know of for your problem.  If your going to
continue to use the component, make the remainder of the download the total
amount of bytes for your preloader to work with, eg: if the preloaded takes 
up
40% of the download make the calculation for your preloader based on 60% of 
the
total.  Also you could use external swf files containing your components and
have them download seperately, have the site down load in sections, eg: imag
es,
script. components,  whatever you want as long as your happy with the result
.
Preloaders are tricky, ive tried 3 or 4 different versions and each have the
re
own problems but i hope macromedia create a new way of having them download
first in a future version of flash, because sometimes they are the BIGGEST
headache, I wish i could swear, and they should be looked at as a future sta
ple
of the net untill connections become super fast.  Also if you can get your
hands on a book that tells you how to use the movieClipLoader object you may
 be
able to do the preloader another way, but as usual it takes alot of
experimentation to understand exactly how it will fit into your site.  Good
luck.