Bug 38867

After the installation I get the very known "Read error" message from the boot1 stage of the boot process. The cdrom kernel, in the installation, recognizes the harddisk as:
 38166MB 77545/16/63 at ata2-master UDMA100 (I've a SEAGATE BARRACUDA IV in the first canal of a offboard Promise Ultra100 TX2 ide controller)
and fdisk "says" that the disk is ad4 and his geometry is 4865/255/63 ( the real geometry ).
I've installed FREEBSD with the "don't modify the MBR" option because I use BootMagic6.0 as boot manager. The FREEBSD partition begins in the 4th Gigabyte of the HD ( < 1024 cilinder ), Partition Magic says that the partition begins in 8048565 (LBA) 501/0/1 (CHS) and ends in 16707599 (LBA) 1039/254/63 (CHS). These LBA values are equal in Partition Magic and in fdisk. The slices that i've created are:
ad4s4a / UFS Y 300MB
ad4s4b swap 150MB
ad4s4e /var UFS+s Y 300MB
ad4s4f /usr UFS+s Y 3500MB
I've obtained the boot sector (8048565 sector) of the freebsd partition  
and observed that is equal that the /boot/boot1 file, they shouldn't be different?.
I've tried to modify the geometry that fdisk uses, using the "change drive geometry option" but fdisk says "incorrect drive geometry".
I would like to know: 
A) is there any way of activate the LBA geometry in the wd driver flags without recompiling the kernel? this is because i don't have a working FREEBSD
B) is there any way of booting my FREEBSD with a boot disk/cdrom using the "boot: 1:ad(4,a)/kernel" option?
C) could i resolve the problem using something like fdisk and a good disktab description of my HD?

Thank you!