Ashley,
1. Open the .stp file and save as Inventor .ipt file.
2. Start a new inventor part.
3. On the manage tab, pick derive part. Choose the .ipt file that came from the .stp.
4. In the bottom left of the derive dialog is a scale factor.
Kirk A.
Windows 7 x64 -12 GB Ram
Intel i7-930 @ 3.60ghz
nVidia GTS 250 -1GB (Driver 301.42)
INV Pro R2013, SP1.1
Vault 2013