flashing file download at startup

Recently i've had alot of problems with my computer pissing around. Awhile ago whenever i turned my computer on winamp would automatically load at start up (which it wasn't suppose to do). It would always open with a dat file in the playlist called MSIMGSIZ.DAT and it would bring up another little window asking me to download a plugin called "nice mc." Anyway i tried everything to stop this f**king annoying download but it just wouldn't go away. Eventually my brother decided to delete the DAT file which i didn't think was a good idea as their important aren't they??? Anyway it got rid of the annoying little winamp problem but soon enuff other problems arose.
For one, everytime i tried signing into msn messenger (version 6.0) it would say it was unavaliable, i then tried version 4.6 and it let me sign in but it froze up every time i tried instant messenging someone, finally i got 3.6 and it worked fine, thank god.
HOWEVER everytime i tried to check my emails it couldn't find the hotmail site. i tried logging into my internet banking, the same thing happened, i finally realised i wasn't allowed in any secure sites, eventually i found this forum and after searching for awhile found someone with the same problem, it turned out somehow my internet explorer 6 had a cipher strength of 0-bits instead of the usual 128-bits. So i reinstalled internet explorer and bingo! i can now check my emails etc.

Now the problem i'm faced with is this. At start up just as everything has loaded i get a flashing download thingy, i believe it has something to do with the MSIMGSIZ.DAT file (earlier deleted) as right before it started flashing it was asking me to download itself from my own computer?!?! Anyway back to the question, all this annoyance does is keep popping up and dissapearing. All i can make out is that it says "file download" at the top but eveytime i try to do anythin on my computer it prevents it.
I believe this is all centred around the MSIMGSIZ.DAT file so can anyone help me out with this extremely annoying occurence? if u can please get back to me as soon as possible as i really miss using my computer and listening to my tunes :no:

P.S - I'm using windows 98SE, internet explorer 6.0 and have done numerous antivirus checks with norton but to no avail.

Cheers -----> Methamphetabeats