Beginner question about Picard AddOrReplaceReadGroups

[yeppomonkey]

Hi,
I am just starting to learn how to use novocraft and GATK, and I reached a point during my analysis where GATK said my file was not accepted without read groups. I searched the forum and people have suggested to use AddOrReplaceReadGroups from picard. I was looking at the picard source page and I am not sure of some the required options. I am trying to understand as much I can about what I am putting through the various software. But I don't understand some of the options.
Can some one help explain what the RGPU options is ( Read Group platform unit (eg. run barcode) Required). Would I get this RGPU from the raw data? or is this something that comes with the documentation for the sequencer?
The exome I am analyzing was sequenced by illumina.
Any help would be very appreciated. Thanks
Not sure if this is useful, but here is the first few lines of my data before alignment:

@HWI-ST132_0459:8:1101:1113:1946#GGCTAC/1
ATTAGAAAAGTAGATTCACATGGTTTTCCACATGTTAGAGGAATTGATAGAATTCTATTTGAACAAAGGACAGTGTTTAC
AAATAATAGCAATGCCATAT
+HWI-ST132_0459:8:1101:1113:1946#GGCTAC/1
ffffffafd^deeeeaaT`adddddac\Vceeeeefff`fbeee`]KK][c_bc^dad_d]`ddZLKYYUcccY^c_ac_
b]WabY_]__NZ[[ZcccUc
@HWI-ST132_0459:8:1101:1247:1955#GGCTAC/1
TAAATAATTTAAATTTCTGATCATAGCCTATTTTTGATATCACAAGGATGACGTCTTGATCTGATAGGAAGGATAAGATA
ACAAGAGGGCCTAGACTAGT
+HWI-ST132_0459:8:1101:1247:1955#GGCTAC/1
gfgfggggggggggggggggggggfggggdgfegggefggggfgegeegegggcggggcgggecggg\eeeecdeegfee
ggeggaaad^e^_acdaYd^
@HWI-ST132_0459:8:1101:1059:1956#GGCTAC/1
AGTAATGACTTAAATAGACATTCTAATGTGGTGCAAAGCTCACGACTCAATATTGAGTACAAAAAAAAAGCAAGTTGTAT
GTGTTAGCCCATTCTCACAC
+HWI-ST132_0459:8:1101:1059:1956#GGCTAC/1
gggfggfgggggggggg_gegagdggegeeeegggadefeggegdedggaeaeecddZeeebdccgegg_edTb[eeaee
eeeeedebeeeYbcbf]ccf
@HWI-ST132_0459:8:1101:1227:1985#GGCTAC/1
TGAATGACTTTGAGATATGGTGTTGGCACTGAATTAAGACAGGAGAAGACTACTGGTGATCTAAAAGGAAATAGTGTTAT
AGTAGTAAAGAAGGAATCCA
+HWI-ST132_0459:8:1101:1227:1985#GGCTAC/1
ggggggggggggegggegggegegggggffggfgfgggggggfdgaegdggfgggecggeeeg_edfecedaedbfff`f
egggfeaefeggffcgdgfc
@HWI-ST132_0459:8:1101:1070:1988#GGCTAC/1
cmyers@cgscluster:~/musa/Eurodata$ clear
cmyers@cgscluster:~/musa/Eurodata$ more pt170.fq
@HWI-ST132_0459:8:1101:1113:1946#GGCTAC/1
ATTAGAAAAGTAGATTCACATGGTTTTCCACATGTTAGAGGAATTGATAGAATTCTATTTGAACAAAGGACAGTGTTTAC
AAATAATAGCAATGCCATAT
+HWI-ST132_0459:8:1101:1113:1946#GGCTAC/1
ffffffafd^deeeeaaT`adddddac\Vceeeeefff`fbeee`]KK][c_bc^dad_d]`ddZLKYYUcccY^c_ac_
b]WabY_]__NZ[[ZcccUc
@HWI-ST132_0459:8:1101:1247:1955#GGCTAC/1
TAAATAATTTAAATTTCTGATCATAGCCTATTTTTGATATCACAAGGATGACGTCTTGATCTGATAGGAAGGATAAGATA
ACAAGAGGGCCTAGACTAGT
+HWI-ST132_0459:8:1101:1247:1955#GGCTAC/1
gfgfggggggggggggggggggggfggggdgfegggefggggfgegeegegggcggggcgggecggg\eeeecdeegfee
ggeggaaad^e^_acdaYd^
@HWI-ST132_0459:8:1101:1059:1956#GGCTAC/1
AGTAATGACTTAAATAGACATTCTAATGTGGTGCAAAGCTCACGACTCAATATTGAGTACAAAAAAAAAGCAAGTTGTAT
GTGTTAGCCCATTCTCACAC
+HWI-ST132_0459:8:1101:1059:1956#GGCTAC/1
gggfggfgggggggggg_gegagdggegeeeegggadefeggegdedggaeaeecddZeeebdccgegg_edTb[eeaee
eeeeedebeeeYbcbf]ccf
@HWI-ST132_0459:8:1101:1227:1985#GGCTAC/1
TGAATGACTTTGAGATATGGTGTTGGCACTGAATTAAGACAGGAGAAGACTACTGGTGATCTAAAAGGAAATAGTGTTAT
AGTAGTAAAGAAGGAATCCA

[TiborNagy]

The read group can be found in your sam/bam file. This file is generated by a mapping program (in your case it is novoalign). If you have multiplexed data, then you need to separate the results in your sam/bam file with read group. However if you do not have multiplexed data, does not matter what kind of strings do you add to AddOrReplaceReadGroups.