How do i find out what programs are using my com3 port becuz i cannot connect to netzero?

before i upgraded to vista it was working just fine. i use netzero since my school blocked limewire and other places like myspace. after i upgraded to vista business it keeps saying error 633 another program is using that port and it tells me to do the commat alt delete and end all programs exept the explorer and sys. doin that causes certain things to not work like my volume keys and stuff like that. is there any other way to figure out wat program is using my com3 port. i went to switch ports and a bunch of them came up and only two of them said they were being used. please help cuz this is money out my pockets every month