You might consider running it natively with VDMSound. Since you're running a GF4 video card, you would need to run NOLFB.COM first. You would need to place NOLFB.COM as the first entry in your TOONSTRK.BAT file (if you didn't install NOLFB.COM along with VDMSound 2.10, you will also need to define it's pathway [unless you just copy NOLFB.COM into the game directory]).
ToonStruck seems to be very demanding with audio resources, so you would need to use a plain SoundBlaster instead of a "SoundBlaster 16" (which you would be using in DosBox anyway).
Also, the game runs normally in 640x400 mode, as opposed to 640x480 mode (where it appears in "Letterbox" format), so you might consider manually changing the video configuration to that.
Not sure if the GF4 supports 640x400 in XP...I know the GF3 does.
In any case, I've attached the game's config file. Just download it, change the CD-ROM letter to match your own, and rename it to TOONSTRK.CFG. Set up NOLFB as I mentioned earlier, then run VDMSound on TOONSTRK.BAT
If you haven't already installed VDMSound, you would obviously need to do that first.