Garry's Mod crashes after 10 minutes of gameplay

Processor: Intel Pentium D 2.8 GHz
RAM: 4 GB installed/3 usable, DDR2, 333MHz
Graphics Card: EVGA Geforce GT 240, 1GB DDR5 memory
Operating System: Windows Vista Home Premium SP2

Addons:
Wiremod (with wire extras)
Spacebuild 3
SBEP
Stargate
Carter’s Addon Pack

Recently while playing Garry’s Mod I have experienced crashes if I play single player for as little as 10 minutes. I have a lot of addons, so this is no huge surprise to me. Because of this, I cleaned out my Garry’s Mod folder, only saving the addons listed above and a few maps, and had the folder regenerate and put these back in. However, this did not help. I loaded up a map and opened a spawn list for one of my addons, and it crashed while generating the icons. I found a command called ‘memory’ that shows how much memory the game is using, so I tried making only a few icons generate at a time while using this command to monitor my memory usage. Apparently, these spawn icons are using up ALL of my dedicated graphics memory and then it runs out, causing the game to crash. Now I know that Garry’s Mod uses up a lot of memory, but this is truly insane. I used to be able to do some stuff in single player for at least an hour, however my available memory would be so low I couldn’t even save my contraptions with advanced duplicator, but it would at least last a while. Is there any way I can make Garry’s Mod use my memory more efficiently?

Edit: The crash is the standard “hl2.exe has stopped working”