video editing nightmare

i'm triing to convert some of my vhs tapes to dvd. after 4 days of fustration i finally thought i had it figured out however now it says i don't have enough space on my media (dvd disk). after 4.5 hrs of rendering using the sony software. (i'm using memorex 8x, 4.7gb, 120min) i then decided to switch back to ulead and it said that i have the disk can only hold about 71 minutes of video. now clue me if i'm wrong but doesn't a dvd hold 120 minutes of video

i can't figure out why it doesn't work. i here about people doing it all the time. here is my hardware/software set-up:
leadtek winfast tv2000 xp tv/video card
i have an extra 80gb hard drive
1gb of ram
plextor px712a dvd burner
video card: ati 9500 pro

i have 2 pieces of software
a)sony movie studio dvd/comes w/capture and dvd burning software
b)ulead movie factory 2 se

ulead seams to be better for what i'm doing (no editing, just copiing directly)

i've tried the help feature on ulead software and sony's web site (sony's dbase is next to useless) please help?

thanks in advance

thanks for the tip. i had tried that on the ulead software but it didn't seem to affect it. however i tried the same thing this morning and it worked ok. but by lowering the setting the quality realy took at hit. i'm going to try it on the sony software to see if i get any better results.