who's right? sysinstall or the bios

[dick]

I try to install freebsd-5.4 on a brandnew 250G seagate baracuda 3250823A

Sysinstall states the drive geomery is wrong and chooses a new value.
It ALSO states to fill in the values the *bios* thinks the drive is.

So here's my dilemma:

fbsd values: 30401/255/16 gives 238472MB (almost ok)
bios values: 65535/255/16 gives 514072MB (totally wrong)

What to do?
Can the bios be so wrong?
What must I do?
The drive will also hold a copy of Win98se and WinXP/pro and I don't want any faults to happen by chosing the wrong values.

Please some advice..