Can i use pentax k1000 lenses on any nikon or canon DSLR?

I want to buy a DSLR, though which one I'm still not sure. I read somewhere that even Pentax DSLRs need an adaptor for using the old screw-mounted lenses my k1000 uses. Can I find adaptors for using my lenses on, e.g, a Canon Rebel or a Nikon D3100? I'm a medical student and I don't really have the money for buying new lenses, so any help would be greatly appreciated.

Canon lenses are for Canon cameras
Nikon lenses are for Nikon cameras.

Yes, the old M42 mount screw lenses can be used with an adapter, but with some difficulty

Most Canon FD lenses can be used on EOS camera bodies with adapters, in the strictly manual mode.

Nikon lenses really don't need adapters since the mount has not changed since 1959.

The Pentax K1000 does not use the M42 (screw mount) lens mount. It was the first Pentax 35mm SLR to use a bayonet-type lens mount - the "K" mount which is still used on Pentax DSLRs.

http://en.wikipedia.org/...ntax_K1000

Its possible someone mounted an M42 to "K" mount adapter on the K1000 you have so they could use older M42 mount lenses on it. The adapter locks into place just as a "K" mount lens would so it could be left on the camera.

Just do a search for M42 to Sony or Pentax or Olympus or Panasonic or Nikon or Canon and you'll find an adapter available to allow usage of the M42 mount lens on every modern DSLR.

NOTE 1: There are two M42 to Olympus and Panasonic adapters. One is for the older 4/3 lens mount and one is for the new Micro 4/3 lens mount.

NOTE 2: There are two M42 adapters for Nikon - one for longer focal length lenses that doesn't allow focus to infinity and one with a lens element that allows focus to infinity.

I'm pretty much sure there are no Pentax-K lens mount adapters for Canon or Nikon bodies. Only Pentax-S (M42 screwmount) lenses can be attached to Canon and Nikon bodies using adapters.

Yes, Pentax-S mount lenses do need an adapter also to mount on Pentax dSLRs but since the register of both S and K mounts are the same, the compatibility level remains high. The advantage of sticking to Pentax is that the screwmount lens will benefit from Shake Reduction and focus confirmation, technologies not available during the time the lens was manufactured. Best of all, the lens can be used in Aperture-priority and Manual modes and the lightmeter will work with it, something other brands will have difficulty providing with this setup.

You can get a Pentax K to Nikon converter. The distance from the flange to the image plane is shorter on Nikon's F mount, so you have to get an adapter with a lens inside else you will lose infinity focus (adapters without optics basically function like an extension tube).