Honestly, you shouldn't have to do much.

As long as the media server is gigE and your tape drives are working properly 
(FC ones are pretty easy) I would just make sure you got the buffers set 
something higher than the default:

/usr/openv/netbackup/db/config/NUMBER_DATA_BUFFERS
/usr/openv/netbackup/db/config/SIZE_DATA_BUFFERS

Solaris 10 defaults to 25% of system memory for shared memory.  As long as you 
have more than a couple GB I recommend you use 64 and 262144 respectively.  
Your mpx settings also calculate into how much max shared mem will get used by 
buffers.

We've had great success with our T2000 servers that use FC LTO3.  In our 
environment, some higher end linux/solaris clients over the network can write 
70-80MB/sec cumulatively via a couple jobs multiplexed to a single LTO3 drive.  
We have the 8 core 8GB T2000 systems and they don't even break a sweat (load 
<.5  0% iowait, etc).  We usually load em up with lots of other tasks.

Windows clients just don't backup very fast over the network, even tuned.  
You'll have to mpx several of those clients to a single drive just to meet the 
native write speed.