Buy both. RCT1 is great for playing scenarios, RCT2 is great for building rollercoasters.
Has a very ironic fear of drops
basically I completely agree with Terry, excepyt for the mistake that Cobra pointed out
Although RCT1 is better for scenarios, RCT2 is easier to use and has more features
ONe of the only things RCT1 has over RCT2 is that you have the tool to create hills in game without hours of terraforming work
I hope you have lots of fun with it.