Some peoples computers can't handle multi-clienting as well as others. I know what some people do is:
- Turn off the effects (/effect), as well as any BGM or sound effects (found in ctr+o)
- Try cascading your RO windows so that they aren't overlapping each other. I know a few people with Vista who do this.
- Minimize how many programs you have going in the background. Close anything that isn't necessary or is eating up CPU.