hi

my mbd: intel d865gbf(onboard graphics: 865g)

i installed slackware with 2.4.(forgot) kernel. i ran startx and kde came up but the resolution was 60Hz. after some googling i ran xorgconfig and configured the monitor with settings from its manual. when i was asked for video card i chose i810. then it asked me for video memory i chose 65536kB. doing this much got me 1024*768 at 85Hz. the problem is in the BIOS i've got two options:
AGP Aperture: 64MB(choices like 128MB, 256MB, etc.)
Video Frame Buffer: 16MB(choices 4,8,16)

what should i enter when xorg asks me for the amount of video memory.

AGP Aperture: This is the amount of main memory made avaibable to the gfx card to store texture maps when it's getting low on (onboard) memory. See this for a fuller explanation. It isn't related to the amount of video memory you have. Which brings us to:

Video Frame Buffer: This is the amount of video memory you have. However, while it won't hurt to set it manually, you probably don't need to, as xorg can usually detect it automatically anyway.