The SciFi Channel ran a 30 second sneak peek of SGA season four during an episode of "Eureka" (at approximately 9:43pm).
Fortunately, SciFi Channel ran a small banner about 15 seconds before the sneak peek began, so those watching with their VCR's ready could hit the record button.
The banner running during the sneak peak advertised that Season 4 premieres on Friday, September 28th at 9pm.
Shown during the sneak peek were some previously seen (brief) clips of Sam and another SGA person in Atlantis looking at someone/something; Teyla (laying down) on a gurney, screaming; Dr. Keller in Atlantis looking scared; Sheppard and Ronon running in Atlantis with weapons and aiming at someone/something; Ronon in a forest, looking up; McKay in Atlantis, laying down on something (possibly a gurney, looks like an IV stand in the background), looking scared towards something; and Sam, Sheppard and others in the Atlantis Gate receiving area.
There was a brief scene from a season four episode with Sheppard, McKay, Ronon and Dr. Weir inside a Jumper. (Weir, however, didn't speak during this scene, and sat to the right [camera left] of Sheppard.)
Sheppard (piloting): "Rodney? Ready?
Rodney (standing up in the rear, with a lot of cables dropping down from the ceiling): "Did I mention that this might not work? And that we could either drop out of hyperspace prematurely and end up stranded in the middle of deep space, or quite possibly be vaporized the moment I touch that..."
Ronon (sitting behind Sheppard, growls [you can see the bandage on Ronon's right shoulder from the wound he received in "First Strike"): "Just answer the damn question!"
Rodney (resigned): "Yeah, I'm ready."
Also -- David Nykl appears in next week's episode of Eureka, 'Unpredictable,' based on the commercial that ran for next week.
In this week's episode of Eureka, 'Try, Try Again,' (which had similarities to SGA's 'Hide 'N Seek'), Barclay Hope (SG1's Colonel Pendergast), Vincent Gale (SG1's Nightwalkers), and Don Thompson (SG1's Wormhole Xtreme and Stronghold and BSG) guest starred.