Go here: http://home.wanadoo.nl/~w.speek/speek.htm and pick up 'oggifier' which is a great frontend for oggenc, oggdec and VorbisGain.
Select the VorbisGain tab. The options you want are specified:
Usage: vorbisgain [options] input.ogg [...]
OPTIONS:
-a, --album Run in Audiophile/Album mode.
-g, --album-gain=n Set the Album gain to the specified value. Implies Album
mode
-c, --clean Remove any VorbisGain tags. No gains are calculated
-C, --convert Convert VorbisGain tags from old to new style
-d, --display-only Display results only. No files are modified
-f, --fast Don't recalculate tagged files
-h, --help Print this help text
-q, --quiet Don't print any output (except errors)
-r, --recursive Search for files recursivly, each folder as an album
-s, --skip Skip non-Vorbis or faulty files
-v, --version Display version number and exit
INPUT FILES:
ReplayGain input files must be Ogg Vorbis I files with
1 or 2 channels and a sample rate of 48 kHz, 44.1 kHz,
32 kHz, 24 kHz, 22050 Hz, 16 kHz, 12 kHz, 11025 Hz or 8 kHz.
Wildcards (?, *) can be used in the filename.
The '-g, --album-gain=n' option takes a value in +/- dB, the rest is pretty intuitive, I think.
The VorbisGain options in oggdropXPd are for playback/decoding where you can choose to have the tag values used. OggdropXPd only uses the tags, if they are present, it does not create or modify them at all. It will, however, use the old or new style tags.