Is there any way to get the DLC's out of the game? I do not play them, and they are constantly trying to load in the GECK when I start it up.

You could remove the manually; not recomended. Or get a mod loading program, I recomend FOMM of better, and disable them from the list so they do not load by default. Best part is you can just click them back on if yu want em.

Can't you just disable the .esms in the loader? ("Data files")?

If they're automatically enabling themselves with the GECK, if I remember rightly, it's due to .nam files. In your Data folder look for the files with the extension .nam, then delete them. I can't remember why they appear.