So basically, If I have a 32bit version of a distro on dvd and there is a newer (for example, the suse remasters) dvd delta, can I use the 64bit delta to turn the old 32bit iso into the new 64bit?

What is a "dvd delta"?
The remastered SUSE 10.1 to which you refer seems to be simply a re-issue of 10.1 with bug fixes.
Why not just get a DVD with the 64-bit version?

I already have the suse remaster, I was using it as an example.
A delta is a much smaller cd or dvd image which only contains the changes from one dvd to the last.
To make it clearer, using suse as an example again.
Suppose I wanted to do a fresh install of suse 10.1 and I have the original dvd I downloaded (3.5GB-ish). When suse 10.1 was first released it was a bit of a shambles, especially regarding yast. So it would be better to install the new remastered version with all the bug fixes and online updates, but this would mean downloading another 3.5GB image when not that much has changed.
So I would download the delta.iso, which I would then apply to the original dvd iso (or the disc it was burned to) which then creates a new remastered version. The advantage of this is that the delta.iso is only about 176MB, rather than 3.5GB.

So, the question I was asking, if I had the original suse 10.1 i386 dvd iso, could I use the x86-64 delta.iso and apply it to the original i386 disk to create a x86-64 remastered version?

If I understand you correctly, the orginal is for 32-bit, and the "delta" is 64-bit.
My knee jerk reaction is that this would not work. Unless you find something that says it WILL work, then I suggest just getting a full-up 64-bit version.

Soapbox:
If one has a reasonable high-speed connection, then I think the better choice is a distro which puts a minimal system in place---then install things as you need them using the package manager. For most people, a full install from a DVD is going to give them a lot of stuff they don't need.
KISS

I agree with you, I generally dislike doing multiple disk installs but suse is such a great distro and there doesn't seem to be any other way except net install.
I tried that with the original 10.1 but it wouldn't detect my network (though it did automatically once I did the full install).
The first time I installed was by cd and it used four out of the five for a default install but only pulled a small handful of stuff from discs 3 and 4 and even then most of it I didn't need.
Main reason I went dvd after was to try my new dvd burner.
I also think it is unlikely that I can use delto to go i386 > x86-64 but I thought I'd post just in case anyone else has tried it.

shame:
You may very well have problems trying to install x86_64 on a x86. I believe that you could install the 32 0n a 64 but not vice versa.

I replied to a post of yours that stated you were having install issues with FC6 and it may be the fact you are trying to install x86_64 on a 32 bit machine eh?

I'm trying to install on x86-64
AMD Athlon 64 X2 3800+

I was on 32bit until very recently which is why I have the i386 disc.