Yeah I played on an old Pentium D in the summer till January - I couldn't even load that god-forsaken city / gallows map. If it had more than a dozen trees there was a chance I couldn't load it too, haha.
Just running a core 2 duo, E7500, and doing fine though. That's what, an office processor for a point of sale system these days? I saw it get worse and worse and eventually unplayable for some maps over the course of patches though, which was kind of interesting.
For the record, geforce 450 gts, 4 GB ram