Rashi's psalms will not unpack easily. His comments are stream of consciousness notes. The footnotes by the translator Mayer I. Gruber are physically after each Psalm and the Hebrew is in an appendix. If you were trying to learn medieval Hebrew and fathom the commentary, you need to have fingers in three places in the text at once.
But Rashi's comments do yield some historical nuggets... It seems that the translation of verse 11 - Kiss the son - was not even on the horizon in France the 11th century. Since Rashi specifically comments to preclude Christian arguments, it was surprising to me that he says nothing on this. Apparently (from the footnote) it was Abraham Ibn Ezra a few years later in Spain who read the Hebrew as Kiss the son - (and so Luther and the KJV.) Rashi also adds the word heart to the verse - Arm yourselves with purity of heart.
Arm yourselves with purity - is a nice parallel to the beginning of the poem - parallel to the anointed. I think I could live with this structurally and as a pointer to Christ also. Reminds me of the instruction in 1 John to become pure as he is pure.
The crux for Rashi in verse 11 is whether it is reasonable to suppose that the same people can both rejoice and tremble. I never considered this a problem - rejoicing with trembling is just what one might do when discovering the joy of life in the covenant of the Lord. [update: I wonder just what kind of trembling though - this word seems rare in the Bible and not very positive - but perhaps there is need of an extreme negative to accompany its opposite...] I guess one could say that Rashi is not a translation - since he didn't have to translate anything of course.
Curiously enough there is an answer in this verse in the LXX to James McGrath's recent question - Seize upon instruction or the Lord may become angry!
There was much discussion of psalm 2 among bloggers a year ago. Some links here.