While I am not totally at home in the Pentax lens world, I do know that the kitlens is not a very good lens.
It would be better if you would choose a lens that has better optical quality, if will for sure be noticable in your photos.
The Pentax 16-45mm f4 is a very nice lens. At B&H it goes for around $300 after rebates, I do not know where you live.
The 50-200 is ok, but not more than that. You might want to look at the Sigma 70-300 APO DG Macro instead, it probably has better quality in the same range, and offers more reach, and has a nice 1:2 macro mode.
If you can not find the Pentax 16-45mm f4, a Sigma 18-50 f2.8 EX DC Macro may also be a nice lens to try.
Canon EOS 350D, Tamron SP AF 90mm F/2.8 macro, Sigma 18-50mm F2.8 DC EX, Canon EF 70-200mm f/4 L USM, Tokina AT-X124 Pro 12-24mm F4, Soligor 1.7x C/D4 DG Teleconvertor, Manfrotto 724B tripod, Canon Powershot S30