Installation via pacman instead of pacstrap

Question

I am having problems with installing arch.
Having downloaded various iso, I keep getting hit by problems with my CPU hanging at
various stages in the pacstrap process.
This happens when I use an older arch too (i.e. 2012.06-1-archboot-i686) which still has
the graphical installer.
At the moment I am settled on booting a liveCD giving me # uname -a
Linux archiso 3.4.4-3-ARCH #1 SMP PREEMPT Tue Jul 3 15:13:13 UTC 2012 i686 GNU/Linux
Although setting up my network using # dhcpcd eth0
works fine, I have now created myself a mirror of all the base .tar.xz files
Once I have replicated the base .tar.xz to /var/cache/pacman/pkg
running # pacman -S base
goes fairly successfully for a while, but eventually falls over with CPU hangs as well.
# pacstrap
seems unable to use my pkg cache though.
Is it possible to adapt pacman so that it can do the job of pacstrap? (Or perhaps be
more successful with # pacstrap -c )
And what might be causing the CPU hangs?
Thanks,
Derek
p.s.
Doing these steps:
mount /dev/sda3 /mnt
mount /dev/sda5 /mnt/home
mount /dev/sda6 /mnt/pkg
cp /mnt/pkg/mirrorlist /etc/pacman.d/mirrorlist
mkdir -p /var/lib/pacman/sync/{core,extra,community}
tar xzf /mnt/pkg/dbs/core.db.tar.gz -C /var/lib/pacman/sync/core
tar xzf /mnt/pkg/dbs/community.db.tar.gz -C /var/lib/pacman/sync/community
tar xzf /mnt/pkg/dbs/extra.db.tar.gz -C /var/lib/pacman/sync/extra
actually this time it fell over at untaring community.db.tar.gz
BUG: soft lockup - CPU#1 stuck for 23s! [loop2:151]
Process loop2...
perhaps I should have kept this in noobie

Answer 1

I am trying to do two things...
1) install a version of arch on my computer as the bootable o/s (on HDD)
2) save bandwidth as i am on a limited tarrif, and as pacstrap normally fails part way through the downloading packages stage it makes sense to be able to continue from the place i have already got to ( and hopefully get further ).
3) was hoping that step 2) could be eliminated by installing from a local cache/mirror - but this seems to be only possible with pacmap, not pacstrap
=========
more info relating to my h/w
Have run 30+ passes of memtest86 with no errors
have done HDD self tests using smartctl (and both long and short diagnoses), again with no errors
If i add kernel options to the netinst liveCD (nomodeset and/or force=mwdma2) then the pacstrap process still freezes, but there are no longer any informative (yet unhelpful) kernel errors like ...failed common READ DMA..... WRITE DMA... cpu lockup
=========
the kernel freezing is the biggest problem as it is only after this point that i can see how far things have got, but cannot use the computer to capture it
And finally to answer the original question - why would i not want to update my pacman db? mainly because i cannot achieve 1) at the moment. Am more than happy to update and fix my system once i can get it to install and run.
Derek