You can do a few things to mitigate coin applications that cause problems:

1. Lower the CPU affinity and process priority. You can do this with task manager right-clicks in Windows if you are going to leave Bitcoin running, or you can make a .cmd file (batch file) to run with the start priority options. CPU is required to validate P2P transaction signatures, and someone could be targeting you specifically with attack transaction broadcasts.

2. If your rotating hard disk is fragmented, that means the disk heads will have to hunt all over the platter to find data, limiting the possible input-output operations per second. You can use defrag programs that completely move and defrag every file, but the new blocks every 10 minutes will again be fragmented. It would be best to give the Bitcoin datadir its own ~40gb disk partition to limit hunting. This problem is solved with a SSD - instead of a limit of 150 IOPS from moving heads, it's more like 40000 IOPS.

3. Monitor RAM usage. I'm not so sure this is an issue. I have Bitcoin Core and Namecoin both running. They use under 400MB each on a 8GB system, and don't impact anything else noticeably.