Getting back in the groove again

I haven't exercised regularly in probably 4 years, and am in horrible shape. I recently bought an elliptical machine (remembering how much I preferred those when I used to go to the gym), and had my boyfriend assemble it for me last night. Well, I tried it today, and it's REALLY hard to do now!! I could only hold on for 5 minutes because my leg muscles were killing me!

How long does it take to get acclimated to a new exercise routine? Thankfully, I'm losing weight by diet alone right now, so I'm not going to give up on this, but it's pretty discouraging.

Any advice or words of encouragement are welcome!