I'd be very impressed if you got anything working on a MTU of 0 or 1, considering that's smaller than an ethernet packet header.

I've done some digging, and for a ADSL connection it appears you should set the MTU to 1428. Higher is not good, as above a certain value (1492 I think) you will get extra packet fragmentation that adds a lot of overhead. The default of 1500 for windows is a particularly nasty one becuase you get both fragmentation and extra overhead (MS chose it as being a nice round number for ethernet, where you can use nice big MTUs without suffering as much).

So Sonyk, I'd try dropping the MTU to 1428. Other ones to try are 1458 and 1492, though I think 1492 gives fragmentation somewhere in the ISP. You should find that it generally speeds things up (less overhead and fragmentation).