The problem is that Lightroom and Photoshop are different beasts. LR is a image processing application, whereas Photoshop is a retouching package.
Simply put. If you have a lot of images, that need to be processed (i.e. Density, colour correction. tonal correction etc.) then lightroom is ideal. It also has a sophisticated cataloging programme that lets you classify your images using keywords, so that they can be cataloged and found. Lightroom was primarily intended to handle RAW images, but it'll also handle TIFF and jpeg as well.
Photoshop on the other hand is a retouching programme, that lets you remove bits of the image you don't want. Improve areas and add other elements to a single image. You can't do any of that in LR.
Photoshop does have a similar application for handling RAW files as LR it called Camera RAW. You can also configure it to work with jpeg images as well.
I would suggest the best course of action for you would be to look at some of the LR tutorials on the web and see if that's the programme you want. If so download the 30 day trial version from the Adobe web site and confirm that's what you want. You don't want to spend your hard earned cash on LR only to find what you really want was Photoshop.
You can download a 30 Day version of Photoshop as well. Bear in mind that Photoshop has a lot of functionality that you may never use or need. I estimate I only ever use about 20% of it's potential. Why, simple I don't need to .
Thje other option to consider is Photoshop Elements. Its a lot cheaper than PS and a lot easier to use. The upside is that a lot of the techniques and methods are common to both Elements and Photoshop. You can take your Elements experience with you if/when you go to Photoshop