Hi:

I've installed eaccelerator as many how-to's says... normal

But after a while, load average starts to grow and grow...
I disabled eaccelerator and everything come back again...

what could the problem be ?

Is there anything in your logs?
Do you store your cache in /tmp (mounted as a noexec partition like it should be)
What does the top of the eaccelerator.php page say?

what logs exactly ?

eAccelerator support enabled
Caching Enabled true
Optimizer Enabled true
Memory Size 16,777,180 Bytes
Memory Available 4,817,520 Bytes
Memory Allocated 11,959,660 Bytes
Cached Scripts 308
Removed Scripts 0
Cached Keys 0

now...

eAccelerator support enabled
Caching Enabled true
Optimizer Enabled true
Memory Size 16,777,180 Bytes
Memory Available 420 Bytes
Memory Allocated 16,776,760 Bytes
Cached Scripts 431
Removed Scripts 0
Cached Keys 0

Looks like it's doing it job, just the avaliable space is filled up pretty quickly. You may want to increase the size of the cache if you have the resources. What are your server specs? specifically ram?

ibm x305, 512Mb RAM