Hi FORGOODNESSAKE,
I hope I haven't missed the boat!!! as it's been a while since you have posted but here is my problem solved...
I am a novice user and I have had this problem (up until 2 days ago), where I was putting my Windows Backups, System Images etc. on my Seagate HDD (no other files.) I could eject using best practice (using safely remove hardware icon) when I hadn't written anything to the HDD (so I don't know if this will apply to you). As soon as the above files were on there I couldn't remove it. I found some 3rd party utilities like Unlocker and Sysinternals Process Explorer but as I really didn't know what I was doing I didn't want to play around with these things, from what I have read these work really well for many people (Article ID: 555665 microsoft). I was totally frustrated so I trolled the net for a long while and I came across a thread in social.answers.microsoft.com/w7hardware from a person called dritch09 who wrote in thread - unable to eject usb - "that the likely solution was a change to the settings of Norton Anti-Virus". It was suggested to switch off the auto-protect scan 'Removable Media Scan' option. As well as doing this I excluded the drive (in my case E:) for Norton to check. Once you do this, apply and save, logout and then login again and see what happens.
I hope this works for you as it has for me - fingers crossed that it keeps on working.
I am using Windows 7 Home Premium, 32 bit.
Good Luck