The graph cannot preview" i recieve this error when i go try & look @ web c?

i have a webcam thats fully working on a another xp sp2 system i went to instal it on my work computer and i recieve the above error message when i use the AMCAP software i tried useing the web cam in windows live msn and i recieve an error stating that my web cam is being used by another program if any 1 one has a solution it wld b greatly appreciated!!!!! (i dont know the brand of the cam, the software name on the pc used to install it is "sevnas"
cheers VIXS