Came home from work the other day and my PC was locked up.  When I tried to reboot, I got a blue screen

After trying the different options, I'm receiving three different errors:

#1 System32\Drivers\isapnp.sys missing or corrupt

#2 System32\Drivers\pci.sys missing or corrupt

#3 The amount of system memory has changed.
          Strike the F1 key to continue, F2 to run the setup utility

I've tried to follow the instructions to fix #1 and #2 but it won't let me access the Windows XP CD to do the necessary repair.  I get a blue screen with info about the errors.

By pressing F2 to run the setup utility, I know that I have 128 MB DRAM.  I was able to use the Diaganostic Program and got the following info:

Error Code 2F00:0119 System Memory Failure

         Read 00FD007DH expected 0000000h at address 08104004h
         Suspected memory component located on System Board at label RIMM1

Everything else checked out OK.

Do I really have all three things wrong or do I need to replace my RIMM1 RDRAM Memory card before I really know what else is wrong?  I'd rather not spend the money on new memory if I don't have to. 

I have replaced Memory Modules in other CPU's so I'm confident I can do it -- I just don't want to unless I really have to.  Also -- can I upgrade to more RAM MB or do I need to buy the same 128 MB.  I haven't looked inside my CPU yet to know if I have another available slot (it's not exactly convenient to access at the moment).

Any help is appreciated.  Thanks.