ugnio: It is possible a firewall/nat router is damaging your dwnld packets. Particularly if you have several of them in the path.

Can you give us a total desciption of your set up: 1. OS version,
2. What firewalls you have,
3. ram, 4. HDD space available,
5. Connection type,
6. Modem & router brand name & model numbers,
7. Where are you trying to connect from (home, school, work, etc.)?

I'm particularly interested in 2, 6 & 7.