Me, Te, Se, Nos
When do these go in front or in the back of a word like: vestirnos or nos vestimos?
They go before a verb when it's a conjugated verb. "Vestimos" is conjugated for "nosotros," so you put "nos" in front of it.
They go after and attached to (1) infinitive forms [-ar, -er, -ir], (2) gerunds [-ando, -iendo], and (3) affirmative commands.
But you could have....
Tenemos que vestirnos
Nos tenemos que vestir.
And you could have...
Nos estamos vistiendo.
I found one of Paralee's lessons on pronouns. Hope you find it helpful, too.
Hope you find this notes useful: http://www.cclscorp.com/Showroom/EPT/pdf/5/EPT5PG.PDF
Those look like Direct object pronouns and you can read about them in the Grammar section on this site.
If you search on the Web for Spanish Direct Object Pronouns you will find lots of information about where to put them and when they come before the verb or are even attached to the verb!!
Here is an "About" link I found and here is one from Study Spanish and I think that one of the "Paralee" lessons surely covers this, too, but I am not sure which one and hope someone else can point you to the whole list of Paralee's lessons.
Luciente pointed out to me that the pronouns mentioned in the context mentioned are "reflexive" pronouns....the kinds I know that one uses with pronominal verbs. So I found one of Paralee's lessons on reflexive pronouns which I hope can help you, too.
Here are a couple of other sites to check out:Reflexive Pronouns at About.com and Reflexive Verbs from StudySpanish.com.