Trendnet router rules table full? Any way to whack it?

I have a Trendnet router (model is TEW 452BRP) and it runs rather well it
seems... most of the time. However, every few days or so, my kids complain
that MSN will launch and just hang on their PC. I noticed this too the other
day, and instead of resetting the router (which was always my previous
advice to them) I looked at the router since I was actually there when it
happened. The router "firewall rules" were chock a block full of MSN rules
to various inside lan addresses... Seems that the router doesn't always
clean them up or purge them?

Obviously, power-cycling the router (they dont have access to the router
admin) is a brute-force solution that isn't so hot when Xbox Live is
happening... Anyone know of any way to what the firewall rules on the fly?
Or force the router to validate the ones it has?

PS- I have UPNP turned on - I know it is evil, but damn, it is convenient
when there are connections that come and go. I suppose I could extend the
DHCP lease time to a long time frame to attempt to cut down on the
variations of rules that get set up...

Is there any alternative firmware for this model that works? DD-WRT and the
like dont seem to be an option.