Adhoc became 11mbps instad of 54mbps

i have loptop(OS: XP) and stational(OS: XP) pcs

cabel with internet is in stational pc.
im sharing internet with belkin 54g usb adapter.

it was 54mbps until i connected one more pc ( my gf's loptop(OS: Vista) )
from then my internet became 11 mbps when i connect to the adhoc.

any ideas how to fix that?

Also, i have almost 0 internet when my sister is playing sims 2 on stational .

any ideas how to fix that too ?

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is her wireless set up as 802.11b? A b router on a g system will slow it down.

Generally, adhoc wireless mode is limited to 80211b at set by the 80211b & 80211g standards.

web article about adhoc limitations