No, it should be: Post thou thy desktop, because thine is for words that begin with a vowel sound. I believe the command+you order was used a lot in old English.

You is plural / formal polite; thou is singular and grew to be considered rather impolite outside of parent/child type of relationships. Obviously it ended up out of favor altogether, and "you all" has taken the place of plural "you".

Well, it's the second person objective plural. The second person nominative plural is ye.

Are you sure? ``You all'' has a literal Dutch counter part (jullie allemaal) but the second person plural (jullie) never lost its meaning as second person plural. The addition `all' here simply adds emphasis.
As a random bit of trivia, the Dutch polite/deferential form, U (may or may not be capitalized, depending on how formal you want to be - it's always capitalized when addressed to God), is actually third person singular grammatically, although most people seem to think it's second person singular. You can tell from irregular verbs and the (lack of) change of declension when the word order is inverted.

X-G: do you happen to know more old English grammer like that? I'd love to know more... I've been trying to find out some old Dutch grammer as well, but it seems hard to come by.

Actually, it's the bear from Bo Selecta! (An English comedy show, very twisted).

I like them indeed. I picked it from somewhere the net a year ago, could not say exactly where though.

TWM is teh ultimate!
Simple and uncluttered.
edit: oops, i probably should have let this die...