A tech told you that your Adobe CS3, Photoshop Elements, Canon Software, and Quicken would NOT run under a 64 bit operating system?
I can personally state that Photoshop Elements and Adobe CS (and newer versions Including CS3) run perfectly under Vistax64. There are 64-bit versions of all the latest Canon software and Drivers, and Quicken runs without any problems under 64bit.
If you want to be sure that future CS versions will still work for you, you can see their FAQ at http://www.adobe.com/products/creativesuite/trial/faq/ . Basically, if you own the software, then you may download and activate the trial version of it. So, say you bought CS5 2 years from now, but you accidentally picked up the box that is for 32-bit systems (assuming they release seperate versions) but you needed 64-bit. You should just be able to download and activate the trial using your CD-Key.
In other words; I'm not sure who you use as a tech, but you need to stop asking them for advice.
------- Now here's the REAL difference between 32 and 64 -------
In technical terms, 64-bit Operating Systems address and interface with your RAM (and all other memory) in different ways. 32 bit systems are only capable of addressing a maximum of 4GB of memory, including System RAM, Video Memory, Sound Memory (Yes, there is memory on your soundcard), and various other devices which have dedicated memory onboard.
For those of us who don't know what that means, it simply means that for systems with 4GB of RAM, Windows will "turn off" some of it, so that it can still use the Video Memory, Sound Memory, etc. It will disable an amount equal to your total non-system memory.
Say I have a system running Vista32, 4GB of RAM, a 512MB video card and a 64MB sound card. Add the total non-system memory (Video and Sound cards) for a total of 576MB. Then subtract that 576MB from the 4,096MB (4GB) of RAM. The total usable System RAM (And the total that Windows will see) is 4,096-576=3,520 - a tiny bit less than 3.5GB.
Vista x64 is capable of supporting up to 64GB of RAM, so in other words, you will not lose any practical RAM when using it.
Software compatibility right now (Late 2008) is almost a non-issue. Almost all major software vendors cater to the 64-bit group now, and most (90+%) 32-bit software will run without issue.