One bit of advice: you should check with your friend about your installation of CS3 -- if the friend also is using it, you are actually violating the Adobe license and down the road will likely have problems because of that. You will either need your friend to transfer the title to you or contact Adobe or something, or accept the fact that at some point you will have limited Photoshop functionality unless/until you decide to purchase a "legit" copy.
Another thing is that the Photoshop CSx Camera Raw "plug-in" will not support cameras released after CS is updated to a newer version. I believe that the Canon T1i was released after the release of CS4. What this means is that if you do decide to start shooing in Raw you will need additional software besides CS3 to process your Raw files. One "quick" approach is the Adobe DNG converter, which will convert the T1i Raw files into a format which CS3 can "read" and open into Camera Raw for processing. If you have Lightroom or DPP, you can also use them to process your Raw files and then open them in CS3 directly, not as Raw files but as tiffs (or from Lightroom as psd files or tiffs).
As to whether to use Photoshop or Lightroom, Photoshop is a fully functional image editor and as you go you will want that functionality. Lightroom has powerful Raw editing tools which can also work on jpeg images but lacks the full range of tools the Photoshop editor has.
If you can't get a license transfer for Photoshop from your friend, you have a couple possibilities to get a legit and functional Photoshop app: you can use the educational discount to buy Photoshop at a significant disount (~$300) or you can go the Photoshop Elements route -- a very alternative "lite" version of Photoshop.
Lightroom at ~$100 is a great deal, and for that alone could be well worth having, just realize that it is geared toward "prolific" photogs -- pros and active amateurs who want both a powerful Raw processor and tools integrated around it that make for an efficient "workflow" that offer organization and output capabilities for a volume of images -- doing "fancy" Photoshop image manipulations are great tools to have available but are not the "center" of the workflow.
The Canon Raw software, Digital Photo Professional, is a great place to begin if you are interested in Raw shooting, because it gives you a "starting point" that renders a jpeg-like presentation of your image along with the tools to make that image "more than a jpeg". There are a couple other apps on your CD that are also worth installing and looking at -- EOS Utilities has both the utility to download images directly from your camera (although many of us prefer a card reader for this) and also the ability to shoot "tethered", meaning you can control your camera using a laptop/computer -- this in itself is a great tool to have. ZoomBrowser is also on the CD -- it's a "little" app that can be used for various things -- browsing folders that include Raw images, and some organizational things, as well as downloading images.
I advise you to right away install the Canon apps. Then, I'd suggest a three-prong approach: 1) use the Canon software to start with, 2) start a "learning curve" on using Photoshop (check out Lynda.com and KelbyTraining.com for some very comprehensive tutorials to start with) and then 3) begin reading up on Lightroom -- in fact, I'd suggest this before jumping into the 30-day trial because trying to take on the Lightroom Raw workflow while also learning DPP/Photoshop stuff can be a bit overwhelming because so much about Lightroom involves organizational details. Get a book on Lightroom (look up the authors Scott Kelby, Victoria Bampton and Marting Evening) and begin "soaking things in" until you can't resist).
Hope this helps a bit!
