Is it a problem occuring only in the demo?
I had similiar problems when recording videos of 12.5 for the first time.
If it's a general problem, then there are different factors to consider, at least the ones that worked for me:
1) System performance in general:
If I recall correctly, my old laptop did have some problems with records, causing occasional lag spikes. Can't remember the specs to save my life, must have been Dual Core, 2,2Ghz, but I can't remember anything else. Not like it matters, you'll notice if it doesn't work.
2) Fraps installed on a different drive than the game?
When I looked into this, I saw something about installing fraps on a different drive than the game helping with the performance during records. Did not work for me, but installing Fraps on the same drive as the game worked wonders, never had any problems after that. Still don't know if I simply misread the advice or if my computer is some kind of magic box, but having Fraps and the game on the same drive solved my problem.
3) Assigning specific cores to Fraps and the game:
This is something else I found. In the task manager, you can right-click a currently running application and assign cores to it (if you have a multi-core system, that is). By doing that, you can have different parts of your system process the respective applications. For instance, if you've got a quad core, you can assign cores 1 and 2 to Fraps, cores 3 and 4 to the game. This, however, never worked for me, but that was before I put Fraps onto the same drive, so I don't know. Also, you might have problems assigning the cores due to a lack of rights or the option being grey. If that does happen, I don't know what to do.
Anyway, that's all I can tell you, sorry if it doesn't help, I really don't know that much about all this computer mumbo-jumbo.
Sorry if this should have been in a PM instead, figured I might as well post it here since another person asked!