As a tech there no warranty void for tar or ash on the parts. Over the years I gotten some yellow pc from heavy smokers. With newer pc and cases your best bet is pick up some fan filters for the intact and power supply. Once a month wash them out. As kfor the rest of thepc a once a year cleaning is fine.
general dust will be more of a concern even then just blow the computer out when it gets dusty. The parts and warranty wont be affected by smoke and definitely not by nicotine.
Ive seen some terrible pictures of some computers clogged up with lots of dust and tinge of nicotine colour definitely from a smoker as that was implied for the picture but something like that dust+nicotine colour would need few years easily to settle into a nest. Depends how grotty the person is ;P
Wouldn't worry about it, enjoy your games, enjoy your cigs, blow dust out the computer ones every while like should be done anyway.
Just ash your cig away from the computer to avoid any rogue ash falling and being sucked in by intake fan. The fan will mince the ash anyway but you dont want it floating inside just for moral sake rather than parts failing. Blow i out everyone in awhile.