Memory upgrade

[strangecondition]

Hi everyone,
I would like to upgrade my PCV-RSM21(CE) with new memory,
because it has only 256 Mb

so my question :

do i need two identical memory sticks (so do the motherboard use dual channel?)
or can i put in one 256 and one 512 stick without loosing speed ?

thx

[kee-lo_]

I would use identical, cuts down on problems.

[CyberClaw]

On the subject of memory upgrades I am looking to add yet more memory into my PCV-RS402

I have been looking at the following:

http://www.ebuyer.com/customer/products/index.html?rb=4525206444&action=c2hvd19wcm9kdWN0X292ZXJ2aWV3...

http://www.ebuyer.com/customer/products/index.html?rb=4525171890&action=c2hvd19wcm9kdWN0X292ZXJ2aWV3...

My motherboard is an ASUS P4SD-VL. Will it accept either of the two memory modules Ive been looking into?

My current config is:

Pentium 4HT (Northwood) 2.80C Ghz (What does the 'C' stand for?)
1024Mb 400Mhz PC3200 RAM
Radeon 9600XT
120Gb HDD

Would appreciate any advice you folks could provide on this query.

Cheers in advance