When you give higher priority to an application in Windows XP, you're telling the system to give extra attention or preferential treatment to that program, which may help the program to write to disk faster, refresh faster etc., than it might at lower priority settings.

Within the operating system, priorities exist in a range from 0 to 31. A Normal priority rating assigns a value of 8. Realtime gives an application a priority of 24; and, as such, is the most dangerous assignment to use since it can interfere with Windows XP’s kernel or other operating system processes. (You may not be able to get out the consequences of setting an application this high without rebooting, causing you to lose some data.) High assigns a priority of 13, and Low a value of 4. Abovenormal assigns a value of 13, and Belownormal assigns a value of 6.

So, setting the batch render to "High" AND terminating non-essential processes should provide some performance increases. All that said, your results may vary, depending upon your hardware and other background processes. I would not recommend setting above "High" due the stability isssues (as Vladimirjp unfortunately found out the hard way).

Finally before making any changes in how your OS manages programs and processes or handles memory, I recommend doing a little research just as you would before making changes in Maya. Check the OS helps files, Check the OS web site, etc.

Hope this helps clarify this issue a little more.