Hi, my original configuration: PC2100 256 MB DDR133Mhz CL2 can I combine this with KINGSTON 256 Mb DDR266 PC2100 CL2.5 especially the CL2 and CL2.5 combination scares me? Will this cause problems?

eh?!? Your CL2.5 may work at the lower CL2 latency, otherwise run the CL2 @ CL2.5. Go into your BIOS and see what the computer has set it to and if there is a way you can set the latency timings manually. 98% of the population is asleep. The other 2% are staring around in complete amazement, abject terror, or both.

The BIOS will autodetect the RAM settings & go with the slower of the two, which would be CAS 2.5, but as Zenith said, you may be able to "force" the 2.5 to run at 2.0 by manually adjusting the settings in the BIOS. Do you know the rest of the timing numbers? It's usually something like 2.5-3-3-7...the CAS 2.0 RAM might be something like 2-2-2-6. It all depends on the quality This space for rent

They should work fine but you never really know with odd sticks of ram until you try them! I would stick with the 'auto detect' 2.5 CAS, you wont really see any great improvement in speed dropping to 2 so stick with the slower more stable option. Wizard ICT. Microsoft Certified Professional