I use PS on a Mac and it works just fine. You will need to follow some PS rules for any pixelart to be real pixelart. The n00ntorial thread in the forum has this info on setting PS for pixelpushing.
I had to send back your 2 pieces as NPA because you have anti alias on many details and gradients and several 'tools' that are considered uncool and makes pixelart 'hybrids'.
Any problem or question just ask here.

In the App store there are several freebies that work well, Paint, Seashore among the better ones.
GraFX is great and open source and used by many with loads of additions. See the resource section for that. Highly recommended.

So yea.. welcome to PJ but first you'll have to set up your equipment, k.

ps: shrinking art to fit previews is not allowed. Pixeljoint is all 100% pure pixelart and even a preview file that truncated will rile up the natives.

Have fun, learn a lot, ask questions, get involved and remember that pixelart makes you a better all around digital artist due to the 'pixel level' nature of the artform.