[X-Newbies] "Service attacks" on Mail, Safari, MIE, iTunes, etc.?

[Rodney A.Hoiseth]

Hi there, Wizards and newbies. (I hope nobody minds the cross-post. 
I'll share anything I learn with both lists.)

I have a new Mini, OS 10.3.9 connected to cable with a cable modem from 
the provider. My mini-network (2 Macs, a PC, and  an Oki laser printer) 
is controlled by a Buffalo "Broad Station" router with no firewall 
(hard or soft).

Recently, when using Internet-connected OS X applications (partially 
listed in the subject line), the active window will repeatedly jump up 
and down, like it's resisting a pop-up or something. My instinct tells 
me it's caused by some sort of PC directed malware that can't affect a 
Mac but keeps trying anyway.

Am I way off base?
If I'm anywhere near correct, where can I look for a fix? I'm very new 
to OS X (about a month) so my intuition doesn't function as well as it 
did through OS 9 and I don't know where to start looking.

Thanks for any hints you can offer.

By the way, the Buffalo home page says there's no firmware firewall 
available for my router like there is for the more expensive models, 
but I have reason to believe (after a "slip" by a tech rep) that there 
may actually be one. Does anybody have firsthand experience with 
Buffalo "Internet Sharing" "Broad Station" routers to confirm that one 
way or the other?)

Rodney
in Hayama, Japan

PS I'm fairly certain the jumping phenomenon is not my eyes, and I 
don't use any sense-altering substances other than a beer once or twice 
a week ;-)