How much ram does the puter have?
It could be that the the p75 having Win3.11 is because it doesn't have enought ram.
During POST you should see the ram count, and if the system is less than 16 megs don't even think about installing Win9.x, because IE shell is a resource hog. (Win95 minium install will be okay with our IE shell)
It would be fine if you have 32megs of ram for Win9.x, but you have to check hour hdd to see if it is larger than 500megs.
I douted that your mobo is a PnP, so run MSD at the DOS prompt and write down all of your IRQ & DMA settings for reference during Win9.x installation. (at DOS prompt type MSD )
Also, you could upgrade to Win9.x using piku's method.
Make sure you have all the apropriate divers, because the generic drivers that come with Win9.x may not support all of your hardware.
If you must reformat to install Win9.x, then check your BIOS to see if it support BOOT from CDROM (you can enable boot from CDROM, then you don't need boot disk for Win98). Other wise create a Win9/x boot disk with your CDROM or generic MS-CDROM diver on it.
Once you completed the above steps & backup your important files, then proceed to format your drive.
1. If your system alow boot from CDROM... Boot to a DOS prompt using the boot disk and type FORMAT C: and choses the apropriate disk support.
2. Then reboot the system and install your OS.
3. follow the Wizard to install all the apporpriate drivers.
4. If you don't want to use the BOOT from CDROM in BIOS method.
5. Then Boot the system using the Win9.x boot disk with apropriate CDROM driver to a DOS prompt.
6. At prompt type FORMAT /S to format & copy the system files to your C: partition & make it bootable.
7. At A:/ promt type COPY [cdrom-driver.exe] C: to copy the CDROM driver to C: partition so you don't have to f**k around with the CDROM driver floppy disk.
8. Switch to C: by type CD C:
9: At C:/ prompt run your [cdrom-driver.exe] to install the CDROM driver.
10. Load your Win 9.x CD into the CDROM drive.
11. Switch to the CDROM drive [default is D:] at prompt type CD D:
12. Then type SETUP at D:/ prompt to run the Win9.x install program.
13. Then follow the Wizard to install all your divers & config system.
Good Luck!