"You wield this bladelike beam as if it were a scimitar."
The creature employing the sword-like beam effect of the 2nd-level Drd spell flame blade [evoc] (PH 231) uses it in combat as if the sword-like beam were a scimitar except that...
- When the creature makes attacks with the sword-like beam, he makes them as melee touch attacks.
- When the sword-like beam deals damage, it deals 1d8 points of fire damage +1 point per two caster levels (maximum +10). Note: It doesn't deal slashing damage. This is important for some feats with which a scimitar-substitute could normally be used .
- The spell's sword-like beam is an evocation effect.
- When the sword-like beam strikes a creature with spell resistance, the caster makes a caster level check. Success means this casting of the spell deals damage to the creature as normal for its duration. Failure means this casting of the spell deals no damage to the creature for its duration.
- The sword-like beam is immaterial.
- The sword-like beam can ignite (easily?) combustible materials. Note: This is not given formal rules text and is, in fact, a direct copy-and-paste from the Advanced Dungeons and Dragons, 2nd Edition spell flame blade (Player's Handbook (1995) 260), so take this ignition capacity with the appropriate grain of salt.
Because the sword-like beam is wielded as if a scimitar, the sword-like beam is a martial 1-handed weapon, so wielding the sword-like beam as an off-hand weapon incurs greater penalties than would a light weapon (but this is likely compensated for by the wielder needing only to make touch attacks), and the weapon could be wielded two-handed (although this would provide no benefit to the sword-like beam's damage). I think it's fine to permit a second casting of the spell flame blade to allow the wielder to use two-weapon fighting with a pair of sword-like beams because that's kind of awesome (although, admittedly, druids don't need to be more awesome), but this may trouble more conservative DMs.
This DM would let a creature's special abilities that could be used while wielding a scimitar be used while wielding the sword-like beam (the creature could benefit from the feat Bladebearer of the Valenar (PE 141) or Crescent Moon (CW 113), for example) and were the creature to have picked the scimitar for use with specific special abilities I'd permit the creature to use sword-like beam with those, too (the creature's feat Weapon Focus (scimitar) applying to the sword-like beam, for example).
I wouldn't count the weapon against the creature's encumbrance (the sword-like beam is immaterial, after all). There doesn't appear to be any prohibition against or special effects associated with dropping the effect, being disarmed of the effect, or handing the effect to someone else (be careful anyway). However, a creature not proficient with the scimitar will suffer appropriate penalties for nonproficiency when wielding the sword-like beam.
There are strong arguments both for and against a caster's ability to target the the sword-like beam with spells targeting weapons. In this case, as an evocation effect that creates an immaterial sword-like beam, I'd argue that the sword-like beam is simply too far from an actual, for-reals weapon to be an appropriate target for a spell like magic weapon, but I'd also argue that being able to cast such spells on the effect probably wouldn't unbalance the game. (This latter point is slightly harder to argue if artificer's infusions are available, however.)