Nice work. You should post this on the official forums too (hopefully I didn't scare you off with how I was the other night... wasn't a good night for me to be posting I suppose).
That fast forward in fullscreen thing concerns me though (the fact that it doesn't work for you), since it normally works perfectly fine. Though you weren't meaning to ask about it, I feel compelled to ask... do you have VSync forced on in your video card settings? That's about the only reason I could see fast forward working in windowed mode but not fullscreen (since pSX has to normally disable VSync to fast forward in the first place). Otherwise, I'd be curious to know what on your computer is causing the problem if you ever get it figured out.
Is the resize flicker that occurs whenever you start/stop fast forward a known issue? pSX doesn't normally do that while maximized or in fullscreen or anything like that, but in the pseudo-fullscreen your utility creates, pSX attempts to resize to a window that allows the taskbar and status bar to be shown.
After further testing, it seems that the problem is the utility and behavior in pSX that was solved before v1.13. To explain further... a while back, pSX had problems holding custom window sizes, mainly because whenever VSync was toggled, pSX would snap back to its original window size. Wouldn't normally be a problem, except fast forwarding with VSync on causes it to get toggled off during fast forward, and back on afterwards. pSX Author fixed that problem however, and never again was it seen.
But somehow, your utility is causing the same thing to happen again. When I have VSync on and try to fast forward, pSX tries to snap back to that size I referred to earlier during each toggle (however, your utility seems to catch this within a fraction of a second and resizes it again). With VSync off, the problem doesn't occur at all.
Other than that... while I'm not a fan of stretching images off their aspect ratio (which is what your utility does on my 16:10 monitor... lol), the program seems quite nice. One question I have though is... pSX also has the option to adjust the aspect ratio to many different options. I don't have a game with borders unpacked to test with (just recently moved), but how does your aspect ratio change differ from pSX's? I'm aware of the black border situation, but your program allows a 16:10 (which zero PS1 games run at), so I'm confused exactly what's going on. Using the various different ratio options via the batch files all yield the same "stretched across my whole screen" problem instead of properly adjusting pSX to display with the specified aspect ratio.
Could you please elaborate on the difference of what this utility fixes and what it enhances? The more I read and test, the more confused I am about what exactly you actually set out to accomplish while creating this utility.