I am guessing you want a desktop PC for the Windows world, so a Mac is out Personally I would avoid a touch screen, other than iPad, like the plague. Stay with a main stream PC or Mac for a better value. Most any i5, and definitely i7, based PC running Win 7 (or Mac running Lion or Mountain Lion) will do the job. You would want 8GB of memory with 16GB being a nice thing to have (if it only a little extra money). I would want an solid state drive (SSD) as my first disk. On it you put the operating system, applications, and caches (for apps that will let you define where to put caches). Your data storage (all the folders like documents, music, pictures) would be on a traditional spinning hard disk. These days get a 2TB drive. Then to do all important backups, get an external USB 3 drive that is 2TB or larger (you can get 3TB drives for around $130 at Costco) to do backups. The machine should also have an internal CD/DVD drive for reading software disks, music disks, and burning disks you make.
Look at computer reviews at sites such as CNET.com, NewEgg.com, and MaximumPC.com and others. Look for back to school sales that still might be ongoing!
BTW, sooner or later you need to upgrade PS and LR to newer versions that are supported by the vendor and will run on newer operating systems. You want OSs and apps that run 64 bit....not 32 bit.
