I'm pretty sure I do understand the problem although mentioning Classic Disc Numbers possibly threw it a bit off track - the singles collection /is/ 29 discs on CD, so that's what's expected if you tag against http://musicbrainz.org/release/14fe90cd … 10b0ff3260 with default Picard.
The media player makes a difference because decent ones will understand the disc number and track number tags inside the files independently and can understand that they are the same album and correctly order the tracks regardless of file names/folders. I've no idea what Winamp does these days; but last I used it didn't count as a decent media manager in my book ;-)
Do you want it to be in a single disc, or a single folder? Or both? This means two different things :)
Here are your options
Tagging against 29-CD release as it sounds like you currently are:
1) Default Picard 0.16 with default file renaming string in Options > File Naming (no plugins)
Files: Britney Spears\The Singles Collection\1-01 TrackName.mp3, 1-02, 2-01, 2-02 etc
Inside Tags: Album Title: The Singles Collection Disc Numbers: 1,2,3...29 Track Numbers: 1, 2
2) Default Picard 0.16 with default file renaming string in Options > File Naming AND Classic Disc Numbers plugin
Files: Britney Spears\The Singles Collection (disc 1)\01, 02
Inside Tags: Album title: The Singles Collection (disc 1) Track Numbers: 1, 2
Tagging against single "disc" digital media release:
3) Default Picard 0.16 with default file renaming string in Options > File Naming (no plugins)
Files: Britney Spears\The Singles Collection\01, 02 ... 58 etc
Inside Tags: Album Title: The Singles Collection Track Numbers: 1 ... 58
4) Default Picard 0.16 with default file renaming string in Options > File Naming AND Classic Disc Numbers plugin
Same as above, since it's a single-disc release.
* Classic Disc Numbers is probably NOT what you want/need so should disable it
* If you only care about folders on disc, not the tags - use Default Picard 0.16 behaviour and something similar to default file renaming string. You MAY need to reset the file naming string to default if you had one from an earlier version.
* If you'd rather the tracks to be numbered inside tags AND files as 1 to 58, tag against the digital media release instead of the 29-disc CD one.
So it depends whether you only care about the folders/file names, or you also care about what's inside the tags and you should pick option 1 or 3.
In the Options, it shows up as Versino 0.1, but I've found that the version numbers listed in Options don't necessarily match the actual plug in version.
This can only happen if you have multiple versions of the plugin in both the Picard installation directory as well as one under your users directory. Otherwise it's perfectly reliable and read from inside the plugin file itself.