This is the easiest way I came up with to do that two-finger-tapped arpeggio like in I Come in Peace.
There's not a diagram of it here, but it's in the tab for I Come in Peace on the tabs page.

First, be sure you've got the picking part down. It's standard sweep picking, but the arpeggio's is a little bit of a stretch for some folks. You want to make sure all the notes ring out when you do it. It took me a little while to get it sounding clean, but I'm sure a better guitarist will have no problem with it. The only awkward thing about this particular sweep is that you'll probably want to hold the pick between your thumb and middle finger, so your index finger will be free for tapping. It's weird at first, if you've never tried it, but it feels more natural as you practice. Don't get discouraged when you can't do it, because there's a good chance you won't be able to at first. At least, I wasn't able to.

Next is the fun part - tapping. I had given up on ever even attempting any of Buckethead's tapping, but then I thought, "Hey, if it can be done, I should be able to do it." Well, I was wrong. There's a lot of stuff Buckethead does that I'll never ever be able to do, but this isn't as hard as it sounds. You just tap the first note with your right index finger two full steps above the last note in the sweep, and then hammer on with your pinkie another two steps above that. You've got your pick out of the way already, so it should sound pretty smooth as long as you pick the notes in the sweep close to where you'll be tapping on the neck, like Buckethead does. Descend in increments of a half-step, à la I Come in Peace.

Even after you've got the transition down, though, it probably won't sound right. My pinkie wasn't strong enough to make the note ring out, and whenever I hammered on with it, it just deadened the string. I tried positioning my hand different ways, but nothing really helped, and I figured I just couldn't do it. But then I decided I'd start doing all my tapping with my pinkie, instead of my index or middle fingers. It sounded bad at first, but after practicing just a little while I could do passably well with it. Just practice things like Van Halen's Eruption, Randy Rhoads' solo in Crazy Train, etc. to get your pinkie nice and buff. I was really surprised when I tried this arpeggio after doing all that practicing—it actually sounded sort of like Buckethead!

Once you can do it with ease, this arpeggio adds a lot of life to solos, if it's called for. It may have taken me more than a month to be able to pull it off, but I get compliments all the time now, and I even had one guy ask me if I'd learned it from Buckethead. I said I had, and we talked for twenty minutes about how awesome Buckethead is.