Not necessarily.
First, look for clothes that have a Victorian-era or Wild West-era aesthetic. Corsets, long skirts, vests, high buttoned boots, spats, blouses with a high collar, top hats, etc. Stick to dark earthy tones, mainly browns and reds but blacks and greys are pretty good too.
And it will depend on whether you're going for an "adventurer" look or more of a high society look (i.e. an adventurer would wear pants instead of a skirt whereas a high society look would be very similar to a Victorian lady).
And then add a few technological accessories! Make sure they keep with the aesthetic of the time period, i.e. wood and awesome/gold instead of sleek and silver. Google and Wikipedia can give you ideas.
Good luck, and I hope you have fun at your party! It sounds like fun!