You probably have 512mb of ram but some is probably taken by shared ram used by your video adapter.
Download Everest V 1.51 which is the last freeware version that includes the software module which lists all software installed on your computer and provides all the license key numbers – a great tool which has been deleted from all successive freeware versions. It will give you all your system specs.
Download here from the Utilities section:http://www.oldversion.com
The next thing to do is to follow the "Slow Computer Checklist" which should help speed up your computer to its capacity for speed.http://www.bleepingcomputer.com/forums/t/44690/slow-computer/
Also - make sure your page file is set to be 1 and 1/2 times the amount of ram installed (that Everest shows installed)
Optimize the Page File
"Virtual Memory is the space on the hard disk Windows uses as RAM. The Page File (Pagefile.sys) serves as temporary, virtual memory storage for code and data." - Source
Instructions - Go to "Start", "Settings", "Control Panel", "System", "Advanced" tab, in the "Performance" section select "Settings", "Advanced" tab, in the "Virtual Memory" section select "Change". Change the values to:
- Initial size (MB): 1.5 x the amount of RAM in your system
- Maximum size (MB): 3.0 x the amount of RAM in your system
Then select "Set" and "OK" and reboot.
Windows XP by default is set to use only a Dynamic Page File that can resize during normal system operation, consuming resources and causing file fragmentation. A properly configured Page File will not resize (increase) so long as the Initial size is set large enough. Allowing the Page File to resize for rare unforeseen memory intensive situations will prevent "Out of Memory" error messages from occurring. Any resizing will reset to the default Initial size upon reboot and will not cause any permanent fragmentation of the Page File.
If you experience frequent resizing of the Page File, a permanent solution is to add more RAM to your system. It is a good idea to have at least 1 GB to 2 GB of RAM in a PC today. A simple test to determine if you need more RAM is to use you PC for a whole day without rebooting, then look at the Task Manager (Ctrl-Alt-Delete), Performance tab. If the "Commit Charge - Peak" is ever higher then the "Physical Memory - Total" your system could benefit from adding more RAM. When you change the amount of RAM in your system, you have to adjust the Page File size too.
Also - for maximum configuration:
How to configure paging files for optimization and recovery in Windows XPhttp://support.microsoft.com/kb/314482/en-us