Let's do the maths here, let's start with bandwidth;
You want 100 users watching a live 500Kbps unicast stream, that's 50Mbps - so exactly half of your 100Mbps, assuming all traffic is outgoing and there's no jitter or other traffic such as regular web hits for your landing page/catalogue etc. That's surprisingly close to the bone.
Then you want people to be able to watch recorded material too, if this is allowed to happen during live streaming this will significantly disrupt your live streaming, purely due to the cache management overhead and the effort required to record this live stream for later playback (I assume that's how you intend to do this?).
Now onto the disk, you don't mention how many people you'd like watching recorded content or the bit-rate but let's assume you're sticking by the (quite low by the way) 500Kbps rate and the 1TB comes from a consumer 7.2krpm SATA disk. Chances are that although your system will try to use what little memory is left as disk cache it will not be that successful due to the ratio of content store to cache (I always assume that cache will be 0% effective, it's a good basis to go off), so your disk has to be able to get 50KBps per user, per item of content from a disk that's likely to give you at best 20-25MBps of random read - that should be an easy 25MBps divided by 50KBps, unfortunately it's not that easy as each read is an 'IO Operation', for which those disks are good for maybe 150 per second - so at an absolutely theoretical best you could, if your users know how to make their requests in a way that serves you, support 150 simultaneous playbacks.
Now onto your CPU, while it's a 4-year old consumer CPU given the very minor job of shifting data between buses it should be up to the job, it is a consumer CPU however with few of the technologies used in Xeons to keep your server reliable but I'm again assuming this is of little concern to you right now. 4GB should again be fine, the code you'll need won't need even this and whatever left will be a poor cache in relation to content store but it should hold all your static page content so that's fine.
So in summary, you're going to be hampered by your bandwidth and your supplier's ability to ship that much traffic, even though it's quite low anyway - and your disk won't support many playback streams. Other than that you're fine.
