What can I do without the money to make the laptop faster?

The laptop is 10 years old, the community says overclocking is critical, I just want to keep an eye on my Discord and watch videos (YouTube 720p60 jerky lol)

Can I do something, and possibly install a new OS (if yes, which one) because XP Home is currently on it…

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Intel core Duo T5870 @ 2Ghz

Intel GM45 / 47 chipset - Integrated Graphics

2 GB DDR2 SDRAM in single channel

2x 80 GB HDD

I think there's nothing more to be done. It's just too old.

Also an option

Install a SSHD

Try to make it afloat with a Linux system for old computers. The systems are usually kept very slim and run smoothly even on very old systems. However, you should check whether Discord can be installed in the package sources. But systems with APT and snap package sources have a Discord package ready to install.