My first question is can I simply plug this drive into the new faster
motherboard and have it just boot up and run?
Depends on your power supply. You will need a EPS12V power supply and you will want to get a good one that provides clean power signals if you want stability.
Next, should I get a dual core CPU or just a fast single core? Most
of the load on this server is due to Spamassassin dealing with about 2000 email accounts. Although it also serves up websites that is pretty minor load I beleive since they do not get all that many hits.
Get a dual core cpu with 1MB of cache. spamassassin is not a single threaded process so a fast single core will not benefit it. How do you run spamassassin?
I was told up2date will update this server too 4.4. Problem is that
the Directadmin GUI is a bit touchy. Any modifications to the services its married to could be bad. I really need to talk to there tech support on this.
My new server motherboard is socket 939 and supports DDR 400. It was
a bargin off ebay but appears to work fine. Would I be better off getting a socket AM2 that supports DDR2 or will that make much difference in performance? The 939 motherboard supports a max of 4Gbyte DDR too.
DDR2 does not give any notable increase in performance. In fact, it adds latency which is why it took some time for AM2 to come out. You will probably be much more happy with a DDR RAM system.
I also purchased a Seagate SATA 500Gbyte drive. The 300G PATA drive
is just under half full. I imagine mostly email. Mailboxes for the most part have 50M cap but there alot of them and still adding more. Is there anyway to copy the OS installed on the PATA to a larger and faster SATA drive? I am doubting this since the drives place/mnt in /dev will change.
You plan to run this on a single drive? I guess you don't have any problems with downtime. A SATA drive will appear as /dev/sdx while the PATA drive will appear as /dev/hdx. I don't think you will have any problems with drive order/device names.
I know the best solution is to install CentOS 4.4 on new box, install Directadmin, and then backup and restore to new server but that will result in substantial downtime that I am trying to get out off. Plus a lot of work. The Directadmin install has been heavilly customized and I will need to remember what I all did to it. Actually I may still do that but I would like to move to a faster motherboard first so just maybe the backups run faster.
If downtime is important to you, consider adding an extra drive and running software raid mirrors at the very least for the future. You will get downtime no matter what if you are not going to do a live transfer of data from the old box to the new one. You might as well do a good one like perhaps getting yourself a mirrored drive to install on.
If not, you should be able to create identically sized partitions on the SATA drive and use dd to transfer your filesystems across and attempt to boot up with the SATA drive.