There are 2 ways of looking at this. A) Do you want to use the time to learn how to setup and mic an amp etc and get a bit more experience as to how it's done? If so it will be unlikely that you will actually record anything substantial B) or do you want to actually come away with a recording that you can listen to? If you choose this method you can spend time learning more about editing and mixing as opposed to recording.
2 hours is pretty tight. If you have the means at home, record a bunch of takes of each of the part you intend to record in wav format 44Khz, then burn them to disk and get the engineer to edit them as best he can (cut and splice to get tighter riffs) - then get a quick mixdown. Believe me, it takes a long time to EQ something and set up compression etc. If you go into a studio and have never done so before you will end up blowing the first hour on getting setup and will be so stressed out for the next hour that you won't get anything done properly. IF you are rusty at playing and especially if you are under pressure timewise this is the best method to getting the most out of your studio time.
1) record everything at home DI (via USB or firewire if possible) or through a mic (if you have good hardware) at the highest quality you can muster - bring at least 4 takes per riff - the engineer can edit them and piece the track together.
2) You won't get much time to tweak the drums, just bring the drums as a single track burnt to wav format. If you don't have drum software, download some loops at the correct bpm and use them as guide tracks for keeping time. You can change them at another time.
3) have realistic expectations! DOn't consider recording more than one song, if you do (unless you are Steve Vai) you will end up with nothing good
4) ask can you meet the engineer sooner rather than later to explain what you want to achieve and ask him for tips on how to get the most out of your session. Be very clear about the fact that your playing is a but shaky and you are likely to have many many takes to get something right.
5) When you record at home name each riff and part so they will be easily understandable to the engineer (eg, introtake1, introtake2, bridge1, etc.) - remember they have to be imported into ProTools or Cubase and arranged.
6) Write out a map of the song so you can quickly see where everything is supposed to go - it's amazing how you can forget what's supposed to happen next in a song when you are under pressure for time!
7) If you are going to record anything in the studio, make sure you change the strings on your guitar at least 3 days before the session and stretch them out, then tune it up as best you can (you will have to tune and retune a number of times during the first 3 days of changing strings). Stringing a guitar or even tuning a guitar up in the studio is a HUGE waste of time - IF you choose to record your guitar at the studio
8) Know exactly what you are going to play - all of the melodies and harmonies etc. Having to work out how to play a part will lose valuable time - unless you are an accomplished player with a well trained ear.
9) When you are finished ask the engineer to give you a dvd with the finished track in mp3 format & wav format and more importantly, ask that he give you each indicudual track within the song as a seperate wav file too - that way you can upload them to your computer and play around with them at home (add melodies, solos etc and even mix them into the finished piece) or you can even bring them to another studio at a later date.
Will there be vocals or bass? IF so, you will probably need to consider a second session - that way you canb do guitars and bass one day and vocals and mixing the next.
I'm not trying to daunt you, it's just that I've been there before when I started out and I wasted a lot of sessions amd I approach thing a lot differently now. Now that I can actually play well I just go into the studio and record as quickly as possible so I can spend more time at the mix.
An engineer will disagree because they love the art of recording but I think that you should bring your own wav files if you want to be able to bring something home that you can play to your wife and friends. Hope that helps.