One approach would be to do the Open as Smart Object in thee LR Edit in Photoshop dialog. This will give you the ability to double-click the layer the image is on and it will open in Camera Raw so that you can do "Lightroom-like" adjustments.
But, once your image is in Photoshop you really can do much of what you do in Lightroom using Adjustment Layers. Do a little experimenting with things like Levels, Curve, Hue and Saturation and you will find that doing global adjustments is quite easy with Photoshop. And, Adjustment Layers come with masks, which enable you to selectively apply adjustments like the brushes in Lightroom. Add to that the capabilities of blending modes as ways of making layer effects come out with actually a variety of possible effects, well, you will soon see why Photoshop has set the standard for power in post processing.
Of course, you may be tempted to say "If Photoshop is so dang good, why do I need Lightroom?" then, well, it comes down to the efficiency of Lightroom.
If you really do need to resort to Photoshop with a significant number of your images, then I'd suggest doing some tutorials -- online places like Lynda.com have excellent material (Lynda.com is a paid subscription but offers a free trial to get your feet wet). There are also a whole lot of books available on Photoshop and, again, if it's going to be a serious part of your workflow building up a little library can go a long way. My daughter has been working through the book "Layers" by Matt Kloskowski, which as a pretty easy to follow set of tutorials taking you through all kinds of aspects of these powerful features. You can also get "big books" -- Martin Evening, for example, is an "Adobe Guru" who offers a Photoshop book that is updated for each new release, but you can easily find the CS3 edition on Amazon.com
In practice, I rarely use Photoshop, but my daughter, who goes for the creative processing stuff, uses it a lot from out of Lightroom.
