This is my first post. I am having the same or similar experiences as Ulanthorn (sounds have been slow and low) and r3volution (freezing of rendering and out-of-memory issues in the same home made missions that worked fine on patch 1.54.72888). I performed incremental installs from original disks ARMA2 OA testing the same mission and watching via EVGA Precision display on my G15 Logitech keyboard my Video board loading and Vid Memory usage. These are the revisions tested: 1.50.70996 original then patched to 1.54.72888 then patched to 1.55.75445. The first two revisions had none of the above issues and ran smoothly. Revision 1.55.75445 always experienced major sluggishness after an initial period of normal running with the exception that I would initially see for a moment a rendering of graphics like faces and textures that were very primitive (polygonal heads and blurry textures). I ran through this incremental installation three times and each time the result was the same. I have left my install at 1.54.72888 as the game is not enjoyable at the 1.55.75445. The following are some of the specs of my system. I really enjoy this game.
OS: XP Pro (5.1, Build 2600), Processor: Intel Core 2 CPU 6400 @2.13GHz (2 CPUs)
Memory: 2046MB RAM, Page file: 411MB used, 3527MB available
DirectX Version: DirectX 9.0c(4.09.0000.0904), Graphics Card: NVIDIA GeForce GTX 260
total Vid memory: 896.0MB, Current Display Mode: 1280x1024 (32 bit) (60Hz)
Vid driver: Version 6.14.0012.6099 dated 10/16/2010