I have had the same problem with my pc but i have found that i could fix it without adjusting the j4l something file of sweethome. What i have done is using my gamebooster software that basicly boost the active running software RAM usage and turns of any and most all processes running on windows in the background.. So i got down to thinking if its working for the most recent games thats not suppose to work propperly on my pc then it should work for sweethome3d too.... And heaven behold it works a true charm i can now render in 4th quality renders... The software is free and called GAMEBOOSTER hope this works for you guys too... O by the way when i had my old pc also 512mb ram i could play games that needed about 2GB of ram...