I was thinking of just insalling another drive and just moving some of my data to the new one.
This would be the best option. Assuming you mean RAID 0, you can do it with two different drives but each drive will be limited to the size of the smallest drive. So, if you had a 250GB drive and a 750GB drive, the 750GB drive would be limited to 250GB, giving you 500GB total. RAID 0 gives marginal performance benefits in most situations, and if one drive dies, you lose the data on both drives. You say your first drive is already a few years old. The average hard drive lasts about 5-7 years. I would be hesitant to recommend RAID 0 even if these were both brand new drives, but with one drive already aged quite a bit, I see no reason for you to use RAID 0. Furthermore, setting up your hard drives in RAID would require you to reformat your hard drive and reinstall Windows. This is a hassle at best, and at worst you could lose data if you don't have it backed up. And if Windows came pre-installed on your computer, you may not be able to reinstall Windows without buying a new copy of it.
So, in conclusion, don't use RAID, just add another hard drive.
I'm curious though. 88GB is a lot. Why do you feel you need more space?