Windows 7: Dual boot WXP + W7

Hi Everyone
First of all thank you guys for the excellent advices and detailed tutorials, they are really helpful, I already learnt a lot, but, as always I still have some questions.
After assembling a new PC (based on a Gigabyte Z77 DS3H motherboard) I need a dual boot system, with the option to choose between 32 bit WXP and 32 bit Windows 7. I created a slipstream WXP install CD with all the SATA drivers and used it to put the WXP on a primary partition on a SATA HDD. Then using the Windows 7 install CD I put the Windows 7 on a primary partition on a separate SSD.
Unfortunately when switching the machine on the boot fails every time, unless I go into the BIOS every time and select the WXP-containing HDD as the 1st boot device. After that tha machine starts and offers me the choice between the "Earlier OS" and Windows 7.
Why is that ? Why the BIOS does not remember the boot sequence settings despite saving it ? Why am I greeted with the aforementioned opening choices - which comes from the Windows 7 Boot Manager - and not the WXP opening screen which would say "Microsoft Windows XP Professional" (instead of "Earlier OS") ?
Any help would be well appreciated.

Sounds like you have the Windows 7 HDD pluged to the first sata port on the MOBO, WinXP to the next port.
Check your MOBO manual.

If you wanted to boot via the BIOS you should unplug the other HD/SSD when installing each OS. Then set the HD which you want to boot first as first HD in priority in BIOS setup.

But since you already have a Windows Boot Menu, the HD marked System in Disk Mgmt should be set first in priority to boot.

On some BIOS this boot order might be ignored with the non-System HD trying to boot first. As Theog says you need to change the ports to correct it in this case.

When you installed Windows 7, was the disk containing XP also present in the system? If so, Windows 7 wrote its boot loader files into the XP partition -- even though it was on a different disk. You have to boot from THAT disk because it contains all the boot loader files now.