LeftrightOut said:
Synchronous = UP and DOWN run at SAME speed (512/512. 1024/1024))
Asynchronous = UP and DOWN run at DIFFERENT speed (512/128, 256/64. 1500/512)
Yes, he meant to ask whether or not the connection is full duplex
I've got 512/128 ADSL, and in answer to your question, yes you can upload at 128 while downloading at 512, the catch is there has to be sufficient bandwidth for ACK packets to get through quickly in order to maintain high speeds (it's the way TCP/IP works). This means that you generally need to cap your uploads to leave say 4kb/s upstream available to ensure the downstream doesn't slow down.
Alternatively, you can use bittorrent and flood your connection like it's never been flooded before, then you'll max out upstream and downstream.
Don't expect to surf the web at the same time though