Sharing internet connection

Am wondering if anyone has heard of a program that will automatically allow me to manually manage the bandwidth between 2 computers.
i.e
Connection Speed 1.5MB

My computer is used for gaming and heavy music and video downloading, so needs lots of bandwidth,
My sisters computer is only used for MSN so really a 100k bandwidth would do her fine.
At the moment its split equally between the computers,
Can anything be done so i can share the bandwidth manually?

Please help if you can, as this is really pissing me off lol.
Thanks
KingMBC