Colombian drug lords do not have a common interest with Basque separists in Spain other than the latest terrorist techniques. They all share the common interest of more efficient and deadly results. The drug trade is the financier of a lot of these groups. Getting fixated on one particular group and ignoring the rest is not too wise. They are all terrorists.
What you say is very correct. The IRA for example was funded largely by Americans but armed by Gaddafi and the PLO - the armalites from US gun stores notwithstanding.
I don't accept that Bin Laden and Hussein worked in concert. There may have been limited contact based a limited joint aim (to hurt the US) but Al-Qaeda is as opposed to secular Arabs as it the West. Just as Irish Catholics were happy to accept weapons from a Muslim dictator when they both had a desire to harm the UK, so Saddam and Qaeda may have had limited contact.
But organised, working-hand-in-hand partnership? Not likely.