How does Executive and Legislative Branches protect a congressman from reasonable search and siezure?

http://news.yahoo.com/s/ap/20060523/ap_o...

According to this article a bunch of Congressman are riled up because the Justice Department (executive branch) searched a congressmans' office. I assume they had a warrant for the search? What more do they need? Are congressmen and their offices exempt from the laws of this land? I thought they we're legal immigrants after all (pun intended).

I know in other countries it's called "parliamentary privelege", which means that the potential criminal must be brought up on charges in the Parliament before being subjected to a criminal investigation. It's how Romanians keep their corrupt officials, and France had a nice scandal or two about that a few years ago. It's just a guess that Congressmen and Senators are covered by something similar. It's designed to keep opposition parties from tying up political opponents in holding cells over BS charges while votes are going on.

Two points about that case:
As a potential democratic voter, they need to string him up quick. I don't want my party tainted by the same hint of evil that Republicans can flaunt with total impunity. I'd like to at least be fooled into thinking that I could vote for the lesser of two evils.

Point 2, they caught the guy red-handed. There is no defense. He needs to resign his seat quick so another Democrat can run in his place instead of hogging the nomination. You can't serve your public service while you're serving time. We need all the Democrats we can get when Bush and Cheney get the riot act read to them with an opposition controlled Congress.