malangi, ACC is the second option on your car, then, since it is not standard equipment in '98. Also, as strange as it may sound to consumers in US, automatic transmission is an option on all '98 Volvos sold here in US.

Regarding the aftermarket CD changer. If you follow the directions I outlined on Ozbrick, you will not be altering any of the original wiring, so the warranty should not be impacted. In fact, I can disconnect my CD changer in a matter of 2 minutes and there will be no sign of it ever having been connected to the head unit. Also, I used an Genuine Volvo mounting bracket for the trunk mounting (I altered the bracket, not the car, bracket costs $13 and I don't care if I voided the warranty on the bracket), so that should also be ok as far as warranty is concerned.

Good luck with your car. I like mine a lot, even though it sometimes seeks my attention by exhibiting minor problems (some major ones have been taken care of under warranty). I like to tinker with it, so it is not a big deal. It drives beautifully and is very comfortable on short and long trips. I also feel better having my family in a Volvo knowing the safety heritage of the brand.