OK, I've got annoyed with not being able to access any web whilst the rest of the house has P2P running etc...

If I block all ports from 1025 to 65534 are there any obvious ones that I'll need to open in order for the web to work in general?

Most games, VoIP and instant messenger apps use ports in that range. For example, MSN uses TCP/UDP 1025 - 65535 for various things.

The best solution for file sharing is a router which supports some kind of bandwidth management. A lot of different routers have various options.

Incidentally, I use ports 443, 80 and 8080 for bittorrent. It helps other people to get around their firewalls to improve my download speeds.

What router do you have? As JJ says a lot of routers have software that mean you can throttle certain IP/MAC addresses and/or protocols and/or ports to certain speeds.

Even if your router doesn't support this sort of stuff out of the box, software like DD-WRT/Tomato gives you those features and cab run on nearly all routers.