The cap hit would be taken by the Redskins, who would absorb his prorated signing bonus. And yes, Samuels would be playing left tackle. He had an off year last year, but based on his first three years, he was well on his way to becoming a franchise left tackle. In fact, he was a Pro Bowl player in 2002. He's one of the top 10 offensive tackles in football.
Rod Gardner may not be a speed demon, but he is a guy who has caught a TD pass every 10 times he has touched the football in his career. His career yards per reception average is 13.3, but before last year, he was averaging around 15 yards per catch. Pre-Steve Spurrier, Rod Gardner averaged over 16 yards per reception as a rookie.
Unless Samuels is included, this deal should not be done though. You don't trade premier defensive linemen for wide receivers. Especially when there is such a drastic drop off at the defensive end position on the team.