Why not just do a 3-gallon batch instead? My reasoning for doing 3-gallon batches is this: I don't know what I'm doing, so there's a good chance my experiments will fail, so smaller = less waste. I've already produced three abject failures--2 gruits and a messed-up brain-dead attempt at an IIPA. That's 9 gallons of waste vs. 15! Also, full boils are better. I did partial boils for my first couple beers, and while the results were "okay" (after several months of aging!), switching to full-boils made for beer that was great right out of the fermentor. I simply *cannot* over-state the importance of doing full boils! Lastly, 3 gallon carboys are cheaper and smaller, so you can experiment more easily and more frequently. I can assure you, you are going to be experimenting A LOT. It's cheaper, and easier to get through 3 gallons of mediocre beer than it is 5 gallons. Bottling goes quicker, and you need less space to store the bottles. Also, you can feasibly brew more often this way, so you can try out more recipes and more ideas, and your turn-around time from when you get amazing new epiphanies to when you can actually apply in brewing will be shorter. You'll also end up with a larger variety of beers on hand to drink, so you don't get sick of each batch. Right now I've got my pick of 8 or 9 different batches of my own homebrew to drink. Some of those batches are crap, but having the variety available lets me pick away at them instead of trying to slog through as fast as possible so there's room to make the next batch.
If you absolutely MUST do a partial boil, take the recipes you like from here, go to hopville.com and use Beer Calculus to scale the recipes--match the original recipe's gravity and IBUs and you should be fine. The Beer Calculus app will automatically compensate for your reduced hop utilization from the smaller (and more concentrated) boils. It's a great little app and makes tweaking recipes a lot more fool-proof.
