Emulator Problem: EPSXE 1.9 running slow in windowed mode

I am troubleshooting for a friend who is having issues with his EPSXE. The emulator runs perfectly in full screen, but the moment window mode is selected (in any resolution), it has serious lag issues. It can run faster if frame skipping is turned on, but of course then we are missing frames. I am wondering if there is any reason why this would be happening or if anybody has some ideas on how to fix the problem. Please let me know so I can get this fixed. Thank you.

I might have a small idea, since its mean to be run at a certain resolution, in windowed I suspect it is being forced to be shrunk, expending cpu power. although, that seems odd that it would lag. Can you give us the specs? What graphics plugin he is using?

Using Pete's DX6 D3D Driver 1.77 (also tried Pete's OpenGL 2.9). Tried at 640x480 as well as 1024x768... fullscreen runs at 800x600.

Also, CPU usage is nowhere near 100% when being played.

I haven't a clue then. Btw, what game is your buddy trying to play? Is it the same with others?

He's trying to play mega man x4... I tried to look up problems with the game and didn't see any. He doesn't have any other games to compare it to, I told him to download some to test, waiting for him to do that.

What operating system is he using? What are his computer specs?

I'll ask him at the next chance and get back to you