ahem.. if the procie is Phenom II X2 550, then GA-M61PME-S2P can support it (Support for Socket AM3/ AM2+/ AM2 processors) but with limited bus speed. the GA-M61PME-S2P rev.1 can support 52 socket AM3 procies, so the notion that it cant support socket AM3 is a misleading information.
(Note) If you install AMD AM3/ AM2+ CPU on AM2 motherboard, the system bus speed will downgrade from HT3.0 (5200MT/s) to HT1.0 (2000 MT/s) spec; however, the frequency of AM3/ AM2+ CPU will not be impacted. Please refer "CPU Support List" for more information.
GA-M61PME-S2P (rev. 1.0) CPU Support List
so, the 4000MT/s bus speed capability of Phenom II X2 550 will just downgrade to 2000MT/s due to GA-M61PME-S2P limitations.