What do you think about this PC?

256 MB is terribly for using things like Adobe After Effects. Integrated graphics are always poor. You're most likely going to need 2 more gigs of RAM. The hard drive is fine, the processor should probably go up. Just because it's i3 doesn't mean it's good. You should probably get a 4 core processor, although you may not need it. If you're going to be doing professional work, you need a professional computer. HD doesn't mean anything, all it means is that it can support high resolution. Resolution =/= performance. Your videos are going to take a long time to load and to apply effects. You can either save yourself a little money now, or you can keep up with the rest of the industry.