A PA-46 pilot suffered several avionics and autopilot malfunctions but continued his approach in bad weather utilizing track guidance from his GPS; breaking out at 400 FT and landing safely.

Narrative

Coming home in 'hard' IMC with fairly heavy wind and mod rain; two miles of visibility and ceilings of 400-500; were given HDG 120 to intercept the ILS; descend to 3;000 with the autopilot armed for approach. The Garmin 530 switched from GPS to VLOC. Tuned and identified the localizer and glideslope was pegged but alive but NO LOCALIZER showed up? So I flew pink line on the MFD. I was probably five miles outside of the FAF at 3;000 right on magenta line. About two or three miles outside the FAF the plane TOOK off at 1;000 FPM ascent. I was overpowering autopilot; disconnected it and the pitch wheel was set (appropriately) by autopilot to climb so by the time I could disconnect autopilot and re-trim I was at nearly 3;600 FT! I quickly got my wits about me and realized there was no LOC; I descended to catch the glideslope while hand flying and trying to stay on the magenta line but went LOW just outside the FAF and got a low altitude alert from the Tower. I said I was correcting and climbed; centered the glideslope and followed the magenta line (illegally; but it was all I could do; short of diverting to a VFR airport); toward the airport. Broke out at 400 AGL and landed. I was not pleased with the autopilot. Did I do something wrong? We have had gremlins like this before.