Thanks for your reply Terry!
I had looked into the troubleshooter but as mentioned can't seem to get the repair working from XP disc so I'm a bit stuck - I'll try to summarize the steps, but there was definitely some mucking about and reworking on my part as well once things departed the normal path :huh: (apologies for length of post in advance, a lot of this i'm trying to recall over the many attempts in the last week or so)...
The PC came with Vista Home Premium (64bit). I followed the steps to shrink the volume (had to do this from the Vista disk manager gui, as the console diskpart running from Vista DVD said something like access denied, which i spotted on a forum somewhere as 'can happen' and not to be alarmed) - then went through the XP Pro (no SP) install process into the new partition.
On first reboot after XP install, my first muck up - i had stepped away from the install and missed the fact the pc had re-booted and ran the Xp disc install again (had bios setup to boot from cd), I assumed something went wrong and tried to reinstall again.
It saw only 1 partition, and I believe 'now' that this was in fact the vista partition - at the time however (to be safe) i quick formated that partition and reinstalled XP. On reboot, of course only Xp now existed and a 2nd partition, no Vista in sight. XP worked fine at this point however.
Realized the mistake above, and followed the adding vista dual boot to an existing xp system. This went through normally and it added XP to the boot menu. XP booted & Vista booted, yay!
Vista was the 2nd OS i checked after the dual boot option appeared, and after completing the setup it then kicked off a 200+Mb series of updates, after which i finally installed EasyBCD and tweaked the XP entry.
After this Vista loaded fine, but XP now gave the BSD (issue with the vista updates??)
I then spent a few hours over the next couple days trying different things - changing the XP 'drive' that EasyBCD pointed to, making sure the 3 Xp boot files were in both partitions just in case, playing with the diskpart in both vista and XP - ultimately making another set of mistakes.
While playing with diskpart I began messing with bootcfg, and I forget the other 2 cmds (sorry, at work right now) but one was playing with the mbr and the other was similar - this ended up giving me invalid partition table errors for a while which neither XP nor Vista repair could fix. Ultimately, I finally found a new partition on a hidden X drive, killed that, reclaimed back that space and things were back to above (where I currently stand today) - Vista boots fine, XP bsd's.
The main frustration is it feels 'close' :| - but the fact the XP repair console or install only recognizes the Vista partition means I can't get over this hurdle [btw, the only reason I know its the vista partition is the size of the 2 partitions is quite different - roughly 300Gb XP to 100Gb Vista].
Sorry for the long winded recount, I hope that helps/answers your questions.
Things I'm trying to noodle around is whether the fact the XP partition is partition 1 and sits 'ahead' of the Vista one - is that an issue? Is the Vista 64 NTFS radically different from XP Pro (32bit) and that's why XP can't see that partition (if made by Vista)? Do Vista updates nuke the XP partition (because it is on partition 1)?
My current thinking is to use vista's diskpart to scrap everything, reinstall Xp from scratch, then vista (as going in this direction seemed easier) - but in light of the above questions will this always mess up whenever i do updates? Should i try the other way again (vista then xp) paying attention to the xp reboot this time?
Thanks again in advance for your response!
Edit: Hmm, just thinking of something else - the PC is running off of SATA drives. My XP Pro disc (without SP's) seems to go ahead and install but does not have SATA drivers as far as I know - would that limit the partitions it can see?