If your mobo does only support 400MHz FSB, it'd think that it would just downclock itself or something.
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DFI Lanparty UT NF4 Ultra-D
AMD Athlon x2 4400+
2GB (2x1GB) G.Skill DDR400 Extreme Series
XFX nVidia Geforce 7600GT 256MB xXx Edition
ASUS 16x Dual Layer DVD Writer and 16x DVD Reader
Sony Silver 3.5\" Floppy Drive
Western Digital Caviar 320GB 7200 RPM 8MB SATA
Antec Super Lanboy Aluminium Case
Enermax Whisper II 535W
Maybe. I dunno, you should research it. That's what I think it would do.
__________________
DFI Lanparty UT NF4 Ultra-D
AMD Athlon x2 4400+
2GB (2x1GB) G.Skill DDR400 Extreme Series
XFX nVidia Geforce 7600GT 256MB xXx Edition
ASUS 16x Dual Layer DVD Writer and 16x DVD Reader
Sony Silver 3.5\" Floppy Drive
Western Digital Caviar 320GB 7200 RPM 8MB SATA
Antec Super Lanboy Aluminium Case
Enermax Whisper II 535W