Here ya go...
Qur'an 3:27: "Let not the believers take the disbelievers for friends rather than believers. And whoever does this has no connection with Allah unless it is done to guard yourselves against them, guarding carefully. And Allah cautions you against His retribution. And to Allah is the eventual coming."
Qur'an 16:106: Any one who, after accepting faith in Allah, utters unbelief, except under compulsion, his heart remaining firm in Faith - but such as open their breast to Unbelief, on them is Wrath from Allah, and theirs will be a dreadful penalty.
Big difference from Christianity. When Jesus was rebuked by the Pharisees for hanging out with bartenders, hookers, and tax collectors, he replied "Does a doctor practice his trade among the well?"
Are Muslims presumed by the Qur'an to be so weak in their faith that they can't even associate with non-Muslims? That would be like contemporary Christians only associating with other Christians, only watching Christian TV and only listening to Christian music- oh, wait- never mind.
3:27 doesn't seem to address telling a lie at all, much less a lie under oath. And 16:106 turns on the interpretation of "under duress" which every mullah, imam, or islamic scholar I've been able to find interpret to mean "under threat of death." The rest of it clearly says there will be "wrath from Allah" and "a dreadful penalty" for telling a lie. That hardly supports the position that it is OK for a Muslim to lie in court after swearing on a Koran. Just the opposite in fact.