The only way to properly "hide" tracks is in the
pregap - that's before the first index point of the CD, (so before the first track). The link tells you everything you need to know, and lists a bunch of CDs with examples
Basically when you stick a CD in a player, it looks for index 01 in the TOC - however there is an index 00. Usually it just contains silence, but you can put a track in it (the QOTSA track for instance).
That's the only place you can do it though - you can't do the same thing on track 4, because track 3 would have the index 03, then track 4 would be index 04; it's impossible to put an index in the middle that the CD player wouldn't see, it just reads from 01 to 99. So if you had a track containing two songs and a minutes gap, if you put the 04 marker at the start of the second song, the first song would just be seen as part of 03
Like someone else said, it stops your CD conforming to the proper Redbook standard, but it still works on most modern CD players.
Although "
Reverie" on
Ghost Reveries is
technically in the pregap of track 5, it just gets played at the end of track 4 on any modern CD player - so the CD player will display 'Track 4' until "
Harlequin Forest" starts. However if you go to track 5 and press rewind, it will go into negative numbers and "Reverie" starts at around -1:05, and will be displayed as track 5. Basically it's a pointless exercise now as all CD players will play it in the normal sequence of things - all it does is confuse the display (and the people looking at it). The 00 pregap is the only one that gets ignored.
Steve