ok, it seems like your gonna have to do some researching to find a better psu that fits that pc. i can look a bit for you to see what i find.
as for the gpu, i think i might have found you a card that will fit. it should be better than what came with the pc, but i don't know how good it is in general, maybe someone can take a look.
Newegg.com - XFX PVT86SYML4 GeForce 8400 GS 512MB 64-bit GDDR2 PCI Express x16 HDCP Ready Low Profile Ready Video Card - Desktop Graphics / Video Cards
this is one of the reviews of this product which seemed weird for me to find lol.
"Reviewed By: Ish on 3/4/2009
Rating + 5Rating + 5Rating + 5Rating + 5Rating + 5
Tech Level Tech Level: average - Ownership: 1 day to 1 week
This user purchased this item from Newegg
Pros: I love this card. It was my first card i had purchase for my desktop. I have a inspiron 530s and it fits just right. it was easy to install.
Other Thoughts: I want to say thanks for NEWEGG for making it easy for me. their price are the best 5/5"
thing is that its listed that the card requires a 350W psu, and it looks like that 530s only has a 250W :/