I am planning a trip to this city in the near future with the thought of renting a place to live for a few months just to have that experience. Can anyone make a suggestion how I might go about this? I want something in the center of town, furnished. I don't want to stay in a hotel that long a time.

http://www.portalsanmiguel.com/

The Trip Advisor forum for SMdA is very active.
Depending on dates and space requirements, I would suggest the classifieds at www.atencionsanmiguel.org or vrbo
There are many rental agents as well.
M (SMdA, Gto.)

There are additional leads to less expensive rentals at www.fallinginlovewithsanmiguel.com
FAQs: r/e and rentals.
M

I found the travelsanmiguel site quite inactive and the vast majority of posts are by less than a handful of folks with commercial interests.
You might want to check:
www.fallinginlovewithsanmiguel.com
www.vivasma.com
www.yahoogroups.com civilsma (the recently resuscitated civilsma3 group
M

The forums at www.fallinginlovewithsanmiguel.com were "hacked" Thursday night apparently by "Turkish girl" who has an international reputation for same.
The host is attempting to reconstruct all.
M

I'm no help (sorry!) but wanted to suggest you read "On Mexican Time" by Tony Cohan is you haven't already, about when he and his wife moved to San Miguel de Allende in the 80's - colorfully written. Have a wonderful visit!

hfl,
Lo siento, but way out of date, lol.
M