I was looking at a VCD on Ebay and the seller left the note “VCD Will play on ANY home computer and most modern DVD players” in the product description.
Does this mean my DVD drive on my PC is guaranteed to absolutely play this disc, is there anywhere I can check? 
And what is a VCD anyway, is it some sort of halfway horse between a DVD and video cassette?
Yep will work fine if you have the right software, should just be a normal cd rom so should work fine in your drive. You can easily get the software of the net if your software doesn’t work. Just play it like a dvd and should be fine.
VCD=Video Compact Disc
Quality can vary, but it can be as good as a VHS tape.
Specifically, VCD is a variant of MPEG encoding. I wouldn’t go so far as to say “most” DVD players can play that format, though. From the units I surveyed, only about 1/3 of them are VCD capable. Making your own VCDs out of AVI or MPEG files is pretty easy. They tend to bloat, though, so if you plan on burning movies you’ve purchased and downloaded, prepare to need two discs for each.
The percentage of DVD players that play VCDs is debatable. I’ve seen estimates as high as 90%. To get a good idea whether your DVD player supports it, check out the compatability list at DVDhelp.com. Bear in mind that the list is user-compiled, so it’s not 100% accurate. To find out for sure, download their VCD sample CD image, burn it to a CD, and pop it in. There may be some DVD players that will play a commercial VCD, but not a burned one, but I think they’re relatively rare.
As far as your computer, unless you’re running something positively ancient, it will play. VCD is an MPEG-1 stream that adheres to certain encoding specifications. A fresh install of even Windows 95 will play MPEG-1 just fine.
Oh, and as to the question of what VCD actually is? It’s a Chinese government standard, adopted in 1993. While we were all buying VHS tapes, Asians had standalone VCD players.
Chinese government-backed manufacturers later developed SVCD to avoid paying royalties on DVD technology. SVCD looks much better than a VHS or a VCD, but not quite as good as a DVD. A movie spans two or three CDs. SVCDs use MPEG-2, just like DVD, only at lower bitrates.
Another Ebay VCD buyer checking in here… the VCDs I bought refused to play on my PC’s DVD drive but play fine on my newer standalone Sony DVD player. I believe that the discs I bought were in the newer VCD-2 format, which seems to have been the problem. My computer’s DVD drive (a Creative PC-DVD 8X) isn’t the newest thing around - from 1999 or 2000. The upshot: it’s not 100% guaranteed to work, depending on the format and your drive. Unfortunately I can’t be of any more help than that. Sorry!
Any computer can play VCDs. If the CD or DVD drive cannot read a VCD CDROM it just means the disc is bad and the problem is not related to it being a vidoe disc. A VCD is just CD ROM and uses the same file structure. If you look for the large video files (usually with .DAT extension) you can play them with any media player, including Windows Media Player. The rest of the information on the disk is not strictly necessary (disc structure, menus etc).
You can record your own VCDs using Nero or other software.
The only devices that can play VCD 1.0, but not VCD 2.0 are standalone VCD players sold in Asia before the 2.0 standard was finalized in 1995. I can’t say what your problem is, but it’s not that. Perhaps something is wrong with your DVD-ROM drive, or else the disc is on the edge between good and bad, and some drives will read it while others won’t.
Whoops. Replace VCD 1.0 with VCD 1.1 in that post. That’s the actual version number of the first generation of VCDs.
Cool, thanks for the advice everyone. The VCD I’m looking at is only £10 anyway so if its more likely than not to run I may just chance it, not really a lot of money to lose sleep over.
To play them on the computer you just use your cdrom or copy to the HD & play from there. You can get a vcd players from download.com if you have a PC.