Thanks for the suggestion. ArtRage doesn't currently have its own temp files except for undo. For virtual memory the Windows pagefile is used, whatever settings you have applied for Windows Virtual memory will be used when there is not enough available free RAM to perform operations.
If this relates to undo, these temporary files are stored in the standard Windows Temporary file location ( wherever that is set to on the particular system ). Saving and reloading the painting will clear the undo cache, so if there's a lot of undo data and performance is slower due to that, that may be helpful.