New change to the NASA rules -- DOM tubing must be used. Older cars with ERw tubing will be gradfathered in. Here's the note.
NASA Rollbar Changes
1/9/2003

Wrom: UQZAAFXISHJEXXIMQZUIVOTQNQEMSFDULHPQQWOYIYZUNNYCGP KYLEJGDGVCJVTLBXF

Memorandum

No new logbooks will be issued after 4/30/03 to any race car that has a cage made from ERW tubing. Cars with cages certified before then will be grandfathered in.

Note: SCCA has a similar rule, but will not issue logbooks after 1/1/2003 for those cars with ERW tubing (according to a phone conversation with their national tech dept.).

Advisory: Use DOM tubing when constructing a cage.