Being port-scanned : is there any relief?

[Kaat]

I run a small personal server. I know getting port-scanned is 'normal' and apparently can't be stopped, but I wish it wouldn't bog down my server so much. As I write, I am being port scanned; Kerio is showing up to 200 UDP ports open and close in sequence, in quick succession. Other uses can hardly access the server. I think my DNS server is the bottleneck.

Any tips for easing the situation?
Thanks!

My details:
PC is Athlon 800MHz 512GB RAM Win98SE (I know, not the best choice!)
Server is Apache 1.3.31 (new version!)
DNS server is Posadis 0.60.4
Kerio Mail Server 5.7.9
Running Perl, PHP, and MySQL.

[Thing]

Do you have a firewall? If so is it hardware or software?

[Son Nguyen]

Install a firewall and block all the ports you don't need so the connections get dropped before they take any more of your system's resources

[Kaat]

Appreciate the replies ..

I do run Kerio Personal, and it is indeed blocking entries. But it seems the mere act of all those ports being opened and closed so rapidly is what's causing the slow-down. I have a feeling there's no good solution, other than a more beefy system and OS.