Make sure you have the appropriate ports forwarded (I think its 1863,6891-6900,6901 but don't take my word) this
site is very useful if you're not to savvy with routers.
If that doesn't do it its probably worth setting your MTU size to 1400 on your router and NIC - you should just be able to dial into your router and make the change there - for the NIC its probably simplest to use DrTcp.