LAN Woes

There ae two things I want to be able to do with my LAN:
What I want to be able to do, is set up a connection where [BC] is just the middleman; where [BC] has no control. [GC] may access anything on [BC] and connect to the [WAN] via the [BC].
PS: [GC] = Good computer (mine). [BC] = Bad computer (office). [WAN] = internet (duh).
- Transfer files
- Share an internet connection
- [GC] connection to [BC]
- Onboard LAN
- Fully recognized
- Base drivers
- Can only access some shared folders on [BC]
- [BC] connection to [GC]
- D-Link 100Mbps PCI card
- Recognized only after driver updates
- Can usually access everything on [GC] that is not password protected
- [WAN] connection from [BC]
- Airlink 1000Mbps PCI card
- Not fully recognized
- XP drivers
- Fully functional
What I want to be able to do, is set up a connection where [BC] is just the middleman; where [BC] has no control. [GC] may access anything on [BC] and connect to the [WAN] via the [BC].
PS: [GC] = Good computer (mine). [BC] = Bad computer (office). [WAN] = internet (duh).