You can use the dos based ramdrive.sys in Win XP by following these steps.
1.start the add hardware wizzard
2.Click on 'Next' on the 'Welcome' screen of the Hardware Wizard.
3.The Hardware Wizard will scan your machine for new hardware.
4.When it finds no new hardware, say YES, you have the hardware in.
5.Go to the bottom and choose the 'Add a new hardware device' option.
6.Use the 'Install the hardware that I manually select from a List (Advanced)' choice.
7.On the next screen, use the first choice 'Show all devices'. [WAIT!!]
8.From the next screen, choose 'Microsoft' in the list and select the 'RAMdisk Driver'. There is also the 'Have Disk' button - if you click that button, you can manually select ramdisk.inf from C:\WINDOWS\INF
9.Click 'Next' and the Hardware Wizard will install the RAMdisk driver
That installs the hardware so that it now exists on the system. The next thing is to configure it so as to be useful. A quick way may be to add this to your registry and see what happens on your machine. I do not know if this will work for you but I have this in my registry.
Put this into a text file called <whateveryouwant>.reg and click it -> yes
Windows Registry Editor Version 5.00
This ramdrive.sys only supports up to 32 MB but Microsoft also have a sample driver you can download and modify to suit your specific needs. It was mad for 2000 but should be suitable for XP. This will hopefully get you to the 256MB you desire but I do not know since I have not used it.
I noticed nobody has replied to you so I have signed up just for you -- aaaaw
hope this helps give you a start in the right direction.