Improved hardware won't make up for being slow on the trigger and not paying attention. You should be taking those low level instances seriously - its how you're going to learn the right physical-memory for the harder content.
And frankly, most of the BC 5-mans are easier than the Old world instances... BC instances are too linear.
But...
As for addons to improve tanking on a paladin:
At a minimum you should have:
Omen
Tankadin
Decursive
PallyPower
Healbot
Even as a tank, you'll have to toss out decurses and heals and buffs now and then. That's why you want the last 3 I listed. They'll let you do those things without needing to pay attention to that. PallyPower is for the blessings (a paladin without pallypower is not worth inviting), Decursive will take control of your Cleanse/Purify, and Healbot will handle all your healing spells as well as let you bind bandages, buffs, blessing of protection, and other effects to the bars.
Tankadin is useful for studying gear choices - but is not needed during play. You might not need Healbot, but I recommend it anyway - if nothing else its color changing bars are handy visual reminders.
Omen, well, if you're tanking without Omen... you need to reconsider whether or not you want to be a tank. At a minimum you need it there for the others in your group to be able to get Omen and gauge their threat against you. Without the tank having Omen, the DPS and healers are 'shooting in the dark.' As a tank, this will let you know not just when the others have aggro, but how close to getting aggro they are.
You do -NOT- need a damage meter addon. Nobody does, but the tank especially does not need to be misdirecting their attention by paying heed to their DPS. That said, I keep recount around on my machine set to 'Damage Taken' - If anyone else in the group has a value above zero, I consider what I might be doing wrong (baring situation where the critter hits the entire party with a blast of something).
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