You are 3-4. You obviously need to make something happen. Foster is an absolute stud. If the other owner is seriously offering this then accept it. If you are offering, I doubt he's going to accept. If the trade goes through you will be hurting at WR, but decent receivers are much easier to find off the waiver wire than stud RBs. Look at just this past week. Britt, S Johnson, Gettis, Dez Bryant, Bowe - all top performers and possible wire finds. I would do the trade for sure.
QB - A Rodgers, E Manning
RB - A Foster, S Jackson, R Mendenhall, T Jones, R Bush
WR - G Jennings, L Fitz, S Smith (Car), P Harvin, V Jackson
TE - A Hernandez, J Tamme