
If you are have a Mac, look under Users\(Whatever your user account is)\Documents\EA Games\The Sims 2\Projects. If you have a Windows XP, look under Documents and Settings\(Whatever your user account is)\My Documents\EA Games\The Sims 2\Projects. Name it whatever you want, though something like "Nude" would be best. For women, anything will do and for men, choose the briefs. Find the underwear and choose something tight-fitting. If you want to make more than one type of person naked, you'll have to do it separately. Pick the age and gender of the person you'd like to make nude.
If you don't know where to find it, go to Start. Follow the same procedure that you did for the NPC Sim.
Left-click your first Sim and find 'PlanOutfit'. Invite the first Sim to your place, then when he/she comes, just press shift and left-click, and choose 'Make Selectable.' (Make sure you've typed in the cheat code "boolprop testingCheatsEnabled true"). This way, the new Sim can invite your first Sim to his/her house. Make your other Sim build a relationship with the new Sim. After you click on the option of your choice, you will see a nude male/female Sim. Click on 'Plan Outfit,' then on the 'Formal' option. Select your new Sim and click on the clothes rack. Once you've clicked on it, the uncontrollable Sim will now be a controllable Sim. Press the Shift key and left-click on the uncontrollable Sim. When in the 'spawn' button, find 'Toms clothing tester.' This will open a clothes rack. Press the shift key and left-click on any NPC that you want to be nude. Move your Sim to a non-residential lot (like a club or park). Don't worry about the code that appears below. When you're in the game, press Ctrl+Shift+c, and type the cheat "boolprop testingCheatsEnabled true" (without the quotation marks).