I wanna stay at a hostel when I get into Antigua, like Jungle. For Antigua, in general for hostels do you think I need to make a reservation before, or can I just walk up? I would be arriving on the weekend.... thx!

Ordinarily I would have said wait until you get here, but recently I have heard that there are a great many more Europeans coming to Guatemala this year and some people are having trouble finding low to mid-priced rooms, especially on the weekends. If you like a hostel that has on line reservations I would at least reserve the first night.

There are several hostels within a couple of blocks of Jungle. They will find bed for you if full. I wouldn´t worry but some need everything tied down! So--
Drifter

If you can't find a place, go 3 blocks south of Parque Central on 4 Ave Sur to corner of 8 Calle. Go east about 100 feet to # 7 & knock on the door. They rent clean rooms with choice of breakfast or lunch for $10.

Jungle is pretty good, but fills up fast. If you're getting there early it should be fine, but in the afternoon might be a bit risky, so booking might be worth it (you can do it on HostelWorld). But like said above, there are lots of other options around...

What time of year are you going?
Jungle Party and Black Cat (just a couple blocks away) fill up quickly each day. Very good deal - 50 quetzales (about $7 US) including a huge breakfast and internet.
Normally, I'd say just wing it --- but if you are travelling alone and know the specific date you will need a room, then go on ahead and make a reservation.
There are other options nearby -- but if you're travelling alone, they may not be as cheap.

My friend and I went to Antigua two years ago, didn't pre-book, just walked around until we found a place. The hotel we stayed at was cheap ($3/night) or something and it had a kitchen to share. Our whole trip in C. America we didn't book nor stay in a hostel and we found great budget accommidation! Maybe we just lucked out?!?! I don't remember the name of the hotel but it was on the same street as the spanish school primevera just North of the soccer fields and market on the outer part of the city. This is where we studied. Good luck.