Hi Phil & Welcome!
This is common for dialup users unfortunately :-( I suggest you download the latest .439 and peform a clean install, I know 25MB is alot for dialup, sorry you have go through that but this is what is suggested by users and moderators.
If not, I can break up parts of Comodo Internet Security using a nice little tool I just got.

And send you via email. Latest version:
http://forums.comodo.com/feedbackcommentsannouncementsnews_cis/fyi_comodo_internet_security_3557173439_update-t31145.0.htmlCheers,
Josh