No, swati is not the same girl... as said before, the other girl "sheena" in DDLJ is the same girl who is in Kal ho na ho, the one with the two kids that saif ali khan flirts with... notice the voices as well, it is NOT her! Just think about it logically guys, DDLJ was released in 1995... and in that movie she has to be minimum of 20... right?... now 11 years later, that would make her 31.. right?... soooooooooo it's oviously not her!! In fact, the girl in kal ho na ho looked quite aged cause she was the same girl in DDLJ...
the girl in DDLJ her name is Anaita Shroff... if you don't believe me, then check out this link...
http://www.rediff.com/cms/print.jsp?docpath=/movies/2003/oct /17ddlj.htm
Swati in Kya hoga Nimmo ka's real name is Tina Chaudhary, check out this link...
http://ww1.mid-day.com/hitlist/2006/january/127681.htm
Hope that clears everything!
Cheers and enjoy kya hoga nimmo ka!