Shirl,
I've taken that route, but unfortunately can't recall how many steps there were? When exiting the Spagna metro stop, I recall a bit of a walk through a "tunnel". When you exit into the small plaza, turn left to the Spanish Steps. Walk past the fountain and left up the Spanish Steps.
When you reach the top of the Steps, turn left and walk (perhaps?) a quarter mile or so. As Liz mentioned, this is where it gets a bit confusing. I recall a "ramp" or paved pathway (which will be across the street) going uphill. If you take that, you'll end up in Villa Borghese (the Park).
As I recall, at the top of the "ramp" you'll turn right, go past a small Gazebo (or other structure), and then bear left. By this point, you should be able to see the Borghese Gallery.
The office where you'll pick up your reserved tickets was downstairs in the basement and to the right (same area as souvenir shop), and I'm presuming that's still the case. The Luggage check was to the left.
Note that the Borghese Gallery is VERY strict about bags, and you'll have to check Purses, Camera Bags, Daypacks and just about anything else you'll be carrying. NO photos are allowed inside, and there are Guards and CCTV in each room to make sure this rule is followed! The Gardens surrounding the Gallery are beautiful and photos are definitely worthwhile.
You might have a look at This Map as it might provide you with a better view. Use the Spagna Metro stop as "reference".
Good luck and happy travels!