Vista SP1 has lot of protections enabled, which can throttle back network performance while playing a media file. This is for ensuring the CPU is having enough available cycles to play the media nicely. Anyway, There may be noticeable network performance deficits, certainly over gigabit.
Now the steps to turn off it:
Go to START then type regedit and then press enter
then go towards this way HKEY_LOCAL_MACHINE \ SOFTWARE \ Microsoft \ Windows NT \ CurrentVersion \ Multimedia \ SystemProfile \
Then double click on the NetworkThrottlingIndex key then enter FFFFFFFF as the Value data.
when you enter this, the base should set to Hexadecimal
Note: Entry supports values from 1 to 70, and the default is 10. If you enter a numeric value, please make the Base to Decimal rather than Hexadecimal. The higher the number, the more the throttling is weighted in favour of the network.