well i'm working on a dell inspiron 910 right now actually, i was noticing the same error as other posts said about asms and other files after that that are missing, let me tell you that whenever the file is not found and its asking you to input the directory, hte d:\i386 worked for me during the whole installation.
sometimes during the installation is would not pick it up, i would press ok continously and it did nothing. the only way i got it to work is to take out and put the cd back in again, so it can re-recognize it again.
since i have an external cd rom via usb, i would also sometimes disconnect it and reconnect back in so it can refresh the connection.
and other threads that are posted that to check the cd's for scratches are actually true. i replaced it with another oem xp sp3 disc and worked like a charm, i thought it would be the cd that was scratched (although it was still working), but the new one was even faster recognizing the missing files.
it might take you awhile to input all the missing files that it asks you for, but again, like the other posts i saw, just copy and paste d:\i386 to the directory every time during the whole installation and it should work without a problem. and if it doesn't work and it stays looking for the same file. then try the disc replacement, the open and close cd tray, and finally reconnect the usb, even try other usb ports.
hope this helped as it did for me. i'm already on the finalizing part so you
shouldnt have a problem.
happy holidays everyone