The following should work; use it at your own risk, but rest assured
it works for me:
Section "Monitor"
Identifier "Primary"
VendorName "Samsung"
ModelName "SyncMaster17GLsi"
HorizSync 30-85
VertRefresh 50-120
# 640x400 @ 70 Hz, 31.5 kHz hsync
Modeline "640x400" 25.175 640 664 760 800 400 409 411 450
# 640x480 @ 60 Hz, 31.5 kHz hsync
Modeline "640x480" 25.175 640 664 760 800 480 491 493 525
# 800x600 @ 56 Hz, 35.15 kHz hsync
ModeLine "800x600" 36 800 824 896 1024 600 601 603 625
# 1024x768 @ 87 Hz interlaced, 35.5 kHz hsync
Modeline "1024x768" 44.9 1024 1048 1208 1264 768 776 784 817 Interlace
# 640x480 @ 72 Hz, 36.5 kHz hsync
Modeline "640x480" 31.5 640 680 720 864 480 488 491 521
# 800x600 @ 60 Hz, 37.8 kHz hsync
Modeline "800x600" 40 800 840 968 1056 600 601 605 628 +hsync
+vsync
# 800x600 @ 72 Hz, 48.0 kHz hsync
Modeline "800x600" 50 800 856 976 1040 600 637 643 666 +hsync
+vsync
# 1024x768 @ 60 Hz, 48.4 kHz hsync
Modeline "1024x768" 65 1024 1032 1176 1344 768 771 777 806 -hsync
-vsync
# 1024x768 @ 70 Hz, 56.5 kHz hsync
Modeline "1024x768" 75 1024 1048 1184 1328 768 771 777 806 -hsync
-vsync
# 1280x1024 @ 87 Hz interlaced, 51 kHz hsync
Modeline "1280x1024" 80 1280 1296 1512 1568 1024 1025 1037 1165 Interlace
# 1024x768 @ 76 Hz, 62.5 kHz hsync
Modeline "1024x768" 85 1024 1032 1152 1360 768 784 787 823
# 1280x1024 @ 61 Hz, 64.2 kHz hsync
Modeline "1280x1024" 110 1280 1328 1512 1712 1024 1025 1028 1054
# 1280x1024 @ 74 Hz, 78.85 kHz hsync
Modeline "1280x1024" 135 1280 1312 1456 1712 1024 1027 1030 1064
# 1280x1024 @ 76 Hz, 81.13 kHz hsync
Modeline "1280x1024" 135 1280 1312 1416 1664 1024 1027 1030 1064
EndSection
