Is that 1GB RAM, or Hard Disk space remaining? That could make a lot of difference.
If your system's RAM is low, eg less than 512MB of RAM, the system may struggle with video applications like Flash.
If you are struggling with hard disk space, then that can cause performance problems as well.
You say this is an old system so it is possible the video card is an on-board card with the motherboard instead of a separate video card. If so, then the video card shares RAM memory with the systems RAM, and if RAM is small, then this may cause difficulties.
So what I am saying is, we need more details of your system specifications.
How did you do that fresh install? XP needs drivers as well as the Operating System and they have to be installed as well.
I have an old computer that I just did a fresh reformat and clean reinstall of the OS on. I downloaded Flash Player 10.1.53.64, with of course no preexisting flash player version existing in my system.
Now when I use Yahoo especially, my browser hangs for 30-45 seconds (showing 99% of CPU), waiting for the Flash ad to reload. Every click on an email in Yahoo Mail usually produces that freeze. You can imagine how frustrating that is!
I think Yahoo's "abuse" with Flash ads is well documented. But is there a minimum RAM recommended for Flash Player? It's an old computer so I only have 1 GB on it.
WinXP SP2, IE7