Runes and Modifications on Items

Intro
I'm well aware that 'stacking' items stack with 'non-stacking' items, but 'non-stacking' items don't stack with themselves; however, I noticed when trying to upgrade my armor with runes that I seem to have only 2 rune slots. How can I determine which slot a rune will use? Is it a matter of determining which runes are prefixes and suffixes?

Armor Example
For example, I have a Survivor Flameforged Robe of Minor Fire Magic.
Energy +5
Armor: 60
Fire Magic +1 (Non-stacking)
Health +15

If I try applying a Rune of Attunement, I lose Fire Magic +1 for Energy +2. If I try appling a Radiant Insignia, I lose Health +15 for Energy +3.

Weapons
For weapons, are there also 2 item mods I can place on them such as a bowstring and bow grip for a bow? How can I increase the standard limit?

Insignias are prefixes, runes are suffixes. You can have one of each on a given piece of armor.

As for weapons, unless it's inscribable, you can add up to two mods. If it's inscribable (it'll say something like "Inscription: Strength and Honor" or "Inscription: None"), then you can add an inscription for a third mod.

Insignias are prefixes and Runes are suffixes.

Weapons may also have inscriptions, which are also item mods.

EDIT: Verene, I swear your post wasn't there when I clicked 'Post'! :P
Apologies for double answer, then.

weapons have 1 inscription + 2 mods.
the inscription will not be listed in the weapon name, but just below it enclosed in quotation marks.
as for mods, theres 1 for prefix, 1 for suffix, shown in the weapon name. each weapon uses different mods/mod names, so i wont list them all. but you can refer to wiki for them:
http://wiki.guildwars.com/wiki/List_of_weapon_upgrades

and heres some reference pages for armour:
http://wiki.guildwars.com/wiki/Insignia
http://wiki.guildwars.com/wiki/Rune


also, whenever you need information on anything about gw, press f10 in-game or type /help. this will open up a search window where you can search for nearly anything u'll ever need to know.