The thing is I'm playing on a PC and can't pull up the internet while in game and strategy guides seem like cheating.
What OS are you using then? Under Win XP Pro, I play full screen mode and have no problems doing a ctrl+tab to get to desktop from which I can open other apps and check the internet, etc. Alternatively, less immersive, but under WinXP Pro you can play the windowed mode and shift to other apps. And, as previously noted, may not be a 'marker', but you can always add editable notes to the map.
John