I cant enchant these boots with anything! I'm trying to enchant "increases magicka by 20 points" but I can't. Is it because I already enchanted the gloves? Or is it because the boots are not able to be enchanted?

If you choose the boots in the window before you choose any effects, then it will tell you what effects you can put on the boots. Assuming you have Unenchanted those effects from other weapons.

It is possible they can not be enchanted.

Edit, they can be enchanted with some effects

http://elderscrolls.wikia.com/wiki/Thalmor_Boots

I guess they can't be. Thanks!

Boots can have only sneak, carry weight and other walking-related enchantments.

Sneak, One-handed, Elemental Resistance are popular choices.

I use thalmor boots to go along with my mage armor perks and I put fire/ice resistance on them usually and have used sneak/onehanded on my vampire assassin

No boots can be enchanted with fortify magicka. Full list of what enchantments can be placed on which items http://www.uesp.net/wiki/Skyrim:Enchanting_Effects.

According to this:

http://elderscrolls.wikia.com/wiki/Thalmor_Boots

They can be Enchanted. They already have an effect, so I don't know if that has to be removed or not. I tend to bury my Thalmor with their boots on.

Thanks guys! I'll probably just put resistance to magic or something.

I meant fire or frost

hehe

I have usually used the boots for elemental resistance, too. Although, my mage got tired of the metallic chinking sound that the Thalmor boots give off and switched to some fancy soft blue suede shoes (my appellation) from the rude lady in Solitude. She's mean, but is the finest clothier in Skyrim and always has my size in stock.

Although, on my current character, I have been wearing the Nightingale stuff because it looks cool. Wish I could un-enchant and re-enchant those. Alas.

I've not seen any Thalmor boots that already come with an effect, I've always come across the robes with Destruction cost enchant but the gloves and boots are always clean.

I put Fire and Ice resist on mine at 52%. It was the gloves I found hardest to put anything useful on, first enchant with easy with fort magic +69, second there was nothing I wanted, ended up with fortify sneak 45% which is pointless for me. I suppose you could put carry weight for the second

It's very strange how inflexible and confusing the whole you can only put this on that thing is, some make sense like only having fortify unarmed on gloves or whatever but some are bizarre. I think it would have been simpler, if you could put any enchant on any item, so you have fortify one-handed on six items. They should have factored in how powerful you would be with six enchant slots when creating the strength of the enchant perks and potions.