Are there any special issues driving in to Serbia from Hungary?
Just remember that once you venture outside of the larger cites in Serbia all of the directional signs will be in the Cyrillic Alphabet. If you cannot read Cyrillic I suggest you study up a bit. The larger tourist areas will typically have signage in Cyrillic and Latin but once outside teh cities and in the countryside you may find yourself confused. I've driven through the Balkans for many years and you cannot expect to find directional signage of the same quality (and quantity) as you'll find in Western Europe, much less the USA. Have a good road map with you and prepared to get lost a few times.
Agree with the last poster, sometimes you have to make educated guesses while navigating, even with a good map. Learning the Cyrillic alphabet is also a good idea, it only takes a few hours. Your pronunciation doesn't have to be perfect, but it helps if you can recognize certain words that sound similar in Serbian and English but look completely different when written. One example that I can render in this forum is "restaurant", which looks like "PECTOPAH" when written in Serbian but sounds about the same in both languages.
I'll offer the caveat that I was last there in the early 2000's, just after they tossed out that bastard Milosevic. At the time, the roads were in pretty bad shape due to years of neglect and damage from the NATO air war, even on the main autoroutes. Things may have improved, but look out for a bumpy ride in certain areas.
Finally, expect to see some of the most suicidally aggressive drivers imaginable.