I have actually fixed this after a week of trial and error but since I wasn't able to find much of anything about this problem by searching online, I'm posting my fix so I can at least have the satisfaction of perhaps helping someone else down the road.
Problem began when I bought an iPhone and installed iTunes. when I ran it, I got a message saying iTunes couldn't install it's CD burning portion due to the presence of other CD/DVD burning software on the system. and when I plugged my iPhone in via USB, iTunes wouldn't recognize it.
A quick inventory of apps on my PC that had anything to do with CD burning pointed suspiciously at Sonic RecordNow burning software and Sonic DLA. for you newbies like me, DLA treats your CD live a hard drive; you put in a CD that you format specifically for use with DLA and you can then drag and drop files to it, sort of like a thumb drive. I guess this might have been a good idea when thumb drives didn't exist yet :)
Anyway I tried to uninstall Sonic DLA via the Control Panel's Add/Remove Programs interface and it seemed to work normally; but at the end it told me I needed to reboot and when I did so, I'd get BSOD at startup, "Windows has detected a serious problem and has shut down your computer to prevent damage". I had to use Norton GoBack to revert to my pre-uninstall state.
When I'd view the drives in Windows Explorer, I'd right-click and see a check box next to "Enable DLA" but it wouldn't let me uncheck it.
A little web searching taught me that I could go to a command prompt and type "DLA.EXE DISABLE D:: and indeed it would disable DLA on the CD drive. I have a DVD drive also (E:) and it worked there too, but DLA would come back after a reboot.
I also found that if I went to Add/Remove programs and selected the "repair" option for the "Apple Mobile Device Support" program, I could then start iTunes, plug my phone in, and iTunes would recognize it; but again, it wouldn't stay that way. So after a week of Apple still working on the problem and Roxio not replying to my query at all, I decided to take matters into my own hands. I got lucky. Here is what worked:
A brief search turned up copies of DLA.EXE in C:\Windows, C:\Windows\system32\DLA, and C:\Program Files\Sonic\DLA.
" I uninstalled all the Sonic programs on my PC except for Sonic Drive Letter Access. This consisted of Sonic Record Now, which Id already deleted, and Sonic Cineplayer DVD. I cant watch DVD movies on my PC now, but thats another matter for later.
" I copied all those files mentioned above to a thumb drive for safekeeping, then deleted the offending subdirectories.
" There were two DLL files in C:\Windows\system32\DLA that were reported as in use, and I couldnt delete them, though I was able to later (see below).
" I rebooted. No BSOD! Bootup completed normally.
" I ran a registry cleaner, RegCure, which found a whole bunch of related junk that mentioned these files, and it cleaned them out.
" I uninstalled all my Apple products: iTunes, Apple Mobile Device Support, Apple Updater, Bonjour, and Quicktime.
" I also was now able to delete those last two files from C:\Windows\system32\DLA and delete that subdirectory (\DLA).
" Rebooted: no BSOD! Bootup completed normally.
" Finally, I went to Add/Remove Programs in the Control Panel and with some trepidation, clicked to uninstall Sonic Drive Letter Access.
" Rebooted: no BSOD! Bootup completed normally. And no sign of SLA on my CD/DVD drives. iTunes reinstalled normally, no error messages, and it recognizes the iPhone when I plug it in. HUGE sigh of relief!!
So I'm not sure how to open a question and then close it right away, but I guess I'll figure that out. To clarify, I don't need any help on this anymore, just wanted to get it in the database for the benefit of the next guy.